Solid-state image sensing element and its design support method, and image sensing device

ABSTRACT

A solid-state image sensing element has a photoelectric conversion element which converts incoming light into an electrical signal in accordance with an amount of the light, a microlens which is arranged on an incident surface, a light guide which is arranged between the photoelectric conversion element and the microlens, and an insulating interlayer which is arranged around the light guide. The solid-state image sensing element located at a distance (H) satisfies: 
                 H   ·   D       L   ·   P       &lt;       a   ·       N   H       N   L         ⁢           ⁢   for   ⁢           ⁢   0     &lt;   a   &lt;   1         
where L is the distance from an exit pupil of an image sensing optical system of an image sensing device, which mounts an image sensor formed by two-dimensionally arranging a plurality of the solid-state image sensing elements, H is the distance from a center of the image sensor to a position of the solid-state image sensing element on the image sensor, D is the height from the photoelectric conversion element to an apex of the microlens, P is the spacing between the plurality of solid-state image sensing elements, N H  is the refractive index of the light guide, and N L  is the refractive index of the insulating interlayer.

FIELD OF THE INVENTION

The present invention relates to an image sensing device having a zoomfunction and focus adjustment function in an image sensing opticalsystem, a lens-exchangeable image sensing device, a solid-state imagesensing element used in the image sensing device and its design supportmethod, and a device.

BACKGROUND OF THE INVENTION

In recent years, solid-state image sensing elements mainly used indigital still cameras and the like are roughly classified into a CCD(Charge-Coupled Device) and CMOS (Complementary Metal OxideSemiconductor) (e.g., see Japanese Patent Laid-Open Nos. 2002-141488 and2002-083948).

Principal components of the structure of the CCD will be brieflyexplained first with reference to FIG. 28.

FIG. 28 is a sectional view of one pixel of a CCD 1000. Referring toFIG. 28, reference numeral 1001 denotes a semiconductor substrate formedof, e.g., silicon; 1002, a photoelectric conversion element including aphotodiode; 1003, an oxide film formed on the semiconductor substrate1001; 1004, three wiring layers which are formed of polysilicon or thelike and transmit clock signals used to transfer a charge and the likeconverted by the photoelectric conversion element 1002; 1006, alight-shielding layer which is formed of tungsten or the like andshields from light a vertical CCD register 1005, used for chargetransfer, mainly formed under the wiring layers 1004; 1007, a firstprotection film which is formed of SiO₂ or the like and protects thephotoelectric conversion element 1002 and the like from external air(O₂, H₂O), impurity ions (K⁺, Na⁺), and the like; and 1008, a secondprotection film formed of an SiON-based material or the like. Referencenumeral 1009 denotes a flattening layer which is formed of an organicmaterial and reduces the unevenness of the second protection film 1008;and 1010, a microlens for focusing light from an object onto thephotoelectric conversion element 1002.

The flattening layer 1009 reduces the unevenness of a principal surface1011 of the CCD 1000, and also serves to adjust the focal length of themicrolens 1010 so as to form a focal point of the microlens 1010 on thephotoelectric conversion element 1002. Hence, the thickness of theflattening layer 1009 made up of a transparent photosensitive resin isdetermined by the curvature of the lens and the refractive index of thelens material.

Principal components of the structure of the CMOS will be brieflydescribed below using FIG. 29.

FIG. 29 is a sectional view of one pixel of a CMOS 1050. Referring toFIG. 29, reference numeral 1051 denotes a silicon substrate (Sisubstrate), on which a photoelectric conversion unit 1052 serving as aphotoelectric conversion element (e.g., a photodiode or the like) isformed. Reference numeral 1054 denotes an insulating interlayer formedof SiO₂ or the like; and 1053, a transfer electrode which is formed inthe insulating interlayer 1054, and is used to transfer a photo chargegenerated by the photoelectric conversion unit 1052 to a floatingdiffusion (FD) unit (not shown). Reference numeral 1055 denotes wiringelectrodes which are formed to prevent light from entering portionsother than the photoelectric conversion unit 1052 and have alight-shielding effect; 1056, a flattening layer which is formed on asomewhat bumpy surface due to electrodes and wiring layers (not shown)to provide a flat surface; 1057, a color filter of, e.g., red, green, orblue; and 1059, a microlens. The microlens 1059 is formed on theflattening layer 1058. The shape of the microlens 1059 is determined tofocus a light beam coming from an image sensing lens (not shown) ontothe photoelectric conversion unit 1052.

An image sensing system (zoom mechanism) of a digital camera with theaforementioned solid-state image sensing element will be describedbelow.

FIG. 30 is a schematic sectional view of an image sensing system 1100 ofa compact type digital camera. Referring to FIG. 30, reference numeral1101 denotes a first lens group; 1102, a second lens group; and 1103, athird lens group. The first and second lens groups 1101 and 1102 aremovable in the optical axis direction within predetermined ranges forzooming, and the third lens group 1103 is movable in the optical axisdirection within a predetermined range for focus adjustment. Referencenumeral 1104 denotes an optical low-pass filter; and 1105, an imagesensor using a solid-state image sensing element such as a CCD, CMOS, orthe like. Reference numeral 1106 denotes a stop, whose aperture size ischanged by a driving source 1107.

Reference numeral 1110 denotes a holding member of the first lens group1101; 1111, a guide pin that guides movement of the first lens group1101 in the optical axis direction; 1120, a holding member of the secondlens group; and 1121, a guide pin that guides movement of the secondlens group 1102 in the optical axis direction.

Reference numeral 1130 denotes a cam cylinder which has a cam groove1131 for moving the first lens group 1101 in the optical axis direction,and a cam groove 1132 for moving the second lens group 1102 in theoptical axis direction. The cam cylinder 1130 is movable within apredetermined range in the optical axis direction. Note that the guidepin 1111 cam-fits into the cam groove 1131, and the guide pin 1121cam-fits into the cam groove 1132. Reference numeral 1133 denotes aguide pin which guides movement of the cam cylinder 1130 in the opticalaxis direction, and cam-fits into a cam groove 1141 formed in a camcylinder 1140.

When the cam cylinder 1140 rotates by a driving source (not shown), thecam cylinder 1130 moves in the optical axis direction. As a result, thefirst and second lens groups 1101 and 1102 move by predetermined amountsin the optical axis direction while being guided by the cam grooves 1131and 1132 formed in the cam cylinder 1130. With this movement, zooming ofthe image sensing system 1100 is attained.

Reference numeral 1150 denotes a holding member of the third lens group1103; and 1160, a holding member of the optical low-pass filter 1104 andimage sensor 1105. The holding member 1160 axially supports a motor 1161to be rotatable. A male screw 1162 is integrally formed on the motor1161. Since the male screw 1162 is threadably coupled to a female screw1163 held by the holding member 1150, the holding member 1150 movesalong a guide bar (not shown) within a predetermined range in theoptical axis direction upon rotation of the motor 1161, i.e., the malescrew 1162. In this manner, focus adjustment of the image sensing system1100 by the third lens group 1103 is attained.

FIG. 31 is a schematic view of a lens-exchangeable digital still camera.FIG. 31 depicts an example of a camera system in which a tele-photo lens1120 is mounted on a camera body 1200.

The camera body 1200 and tele-photo lens 1220 are coupled via acamera-side mount 1211 and lens-side mount 1221. An electrical circuitsuch as a lens MPU and the like (not shown) provided to the tele-photolens 1220 is coupled to an electrical circuit such as a camera MPU andthe like (not shown) via a lens-side contact 1222 and camera-sidecontact 1212.

When a photographer observes an object via a viewfinder, some lightcomponents of object light transmitted through the tele-photo lens 1220are reflected by a quick return mirror 1201 and reach a focusing screen1202. The object light scattered and transmitted through the focusingscreen 1202 is guided to the photographer's eye (not shown) via apentaprism 1203 and eyepiece 1204.

Also, some light components of the object light are transmitted throughthe quick return mirror 1201, are reflected by a sub mirror 1205, andare guided to a focus detection unit 1206. The camera MPU calculates afocus adjustment amount of the tele-photo lens 1220 on the basis of animage signal obtained by the focus detection unit 1206, and drives alens 1223 of the tele-photo lens 1220.

Upon sensing an image, the quick return mirror 1201 and sub mirror 1205rotate in the direction of the focusing screen 1202, and allow objectlight transmitted through the tele-photo lens 1220 to be incident on toan image sensor 1208. Since the exit pupil position varies depending onthe focal length and the like of an exchangeable lens mounted on thecamera body 1200, a light beam that can be received by pixels of,especially, a peripheral portion of the image sensor 1208 changesdepending on the exchangeable lens mounted.

Light rays obliquely enter pixels of the periphery of a frame of theimage sensor 1208. At this time, as disclosed in Japanese PatentLaid-Open No. 1-213079, if each microlens decenters with respect to thephotoelectric conversion unit, it can guide light rays to thephotoelectric conversion unit. However, when the condition of the exitpupil of the image sensing lens changes, light rays cannot enter thephotoelectric conversion unit and the frame periphery often becomesdark. Such phenomenon conspicuously occurs when the pixel size isreduced. Especially, when an image sensing lens that has a zoom functionand focus adjustment function is used, the phenomenon poses severebottlenecks.

Hence, in an image sensing device that uses an image sensing elementcomprising an on-chip microlens (Japanese Patent Laid-Open No.2000-324505), gain control is applied for respective color components ofan image signal in accordance with lens information of an exchangeablelens and the distance from the center of an image sensing surface, thuscorrecting deterioration of sensitivity and variations of hue due toshading and limb darkening. By applying gain control for respectivecolor components using information associated with the exit pupilposition of an image sensing lens, shading can be eliminated.

Japanese Patent Laid-Open No. 5-283661 discloses a solid-state imagesensing device which includes a light guide between a photo-receivingunit and focusing lens. The light guide of that solid-state imagesensing device is formed of a material with a high refractive index, andlight that has entered the light guide is guided to the photo-receivingunit while being totally reflected within the light guide, thusimproving the focusing characteristics.

Japanese Patent Laid-Open No. 2003-163826 discloses a techniqueassociated with shading correction information of an image sensingsystem including an exchangeable lens. Vignetting data and exit pupilposition data are stored on the exchangeable lens side, andincident-angle dependent data of an image sensing element output arestored on the camera body side, thus realizing shading correction thatreflects the characteristics of both the exchangeable lens and camerabody.

Japanese Patent Laid-Open No. 8-223587 is an example of disclosure of atechnique that pertains to color correction means for preventing a huechange of an image due to chromatic aberration of an on-chip microlens.A change in hue of an image due to a change in size of a focusing spotof the exit pupil projected onto the photoelectric conversion unit ofthe image sensing element depending on the wavelength of light iseliminated using a color correction means that corrects the ratio ofcolor stimulus values of an image signal in accordance with the exitpupil position of an image sensing lens.

However, the shading correction and color correction techniquesdisclosed in Japanese Patent Laid-Open Nos. 2000-324505, 2003-163826 and8-223587 basically electrically correct an image signal on the basis ofthe exit pupil position of an image sensing lens. However, boosting asignal level to an appropriate level by applying electrical gain is toenhance not only signal components but also noise components, resultingin a low-quality image in which noise is conspicuous on thedarkening-corrected peripheral portion.

In case of the conventional compact digital camera, the type of itsimage sensing system is limited. Such limitation will be explained belowusing FIG. 32.

FIG. 32 shows a case wherein an object light beam 1061 enters the CMOS1050 as the conventional solid-state image sensing element at a giventilted incident angle (20° with respect to a central axis 1060 of themicrolens 1059 in FIG. 32). In this case, most light components of theobject light beam 1061 transmitted through the microlens 1059 do notenter the photoelectric conversion unit 1052. The same applies to theCCD 1000 as the solid-state image sensing element.

That is, there must be a given limitation on an angle that the objectlight beam 1061 which exits the image sensing system and enters themicrolens 1010 or 1059 makes with the central axis of the microlens 1010or 1059 (to be referred to as an incident angle of an object light beamhereinafter). The object light beam 1061 must enter the microlens at anangle of 10° or less. In case of the image sensing system 1100 describedin FIG. 30, the incident angle of the object light beam 1061 fallswithin the range from 3 to 9 by zooming.

That is, in case of the compact digital camera using the conventionalsolid-state image sensing element, since its image sensing system islimited to a retrofocus system, the degree of freedom in design of theimage sensing system drops, and a size reduction of the image sensingsystem is disturbed.

In order to solve this problem, even when the compact digital camera orlens-exchangeable camera system is formed using the solid-state imagesensing device having the light guide disclosed in Japanese PatentLaid-Open No. 5-283661 above, the light guide cannot often cause totalreflection depending on the exit pupil position of the image sensingsystem of the compact digital camera or the exchangeable lens mounted onthe camera. As a result, light cannot be sufficiently collected on thephotoelectric conversion unit.

An image capture device disclosed in Japanese Patent Laid-Open No.2000-324505 performs gain adjustment of an image signal on the basis ofexchangeable lens information. However, when limb darkening due to theexchangeable lens is large and the output of the image sensing elementis small, gain adjustment must be done at a higher gain. As a result,noise components are also amplified, and a high-quality image signalcannot be obtained.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovesituation, and has as its first object to provide a solid-state imagesensing element which can improve the degree of freedom in design of animage sensing system in an image sensing device, and has high lightcollecting efficiency according to each image sensing device.

It is the second object of the present invention to obtain ahigh-quality image by improving the light collecting efficiency of animage sensing element in an image sensing device having an image sensinglens with a zoom function or focus adjustment function.

It is the third object of the present invention to realize a digitalcamera system which can obtain a high-quality image and can obtain ahigh-resolution image by reducing the size of each pixel in alens-exchangeable digital camera system.

According to the present invention, the foregoing first object isattained by providing a solid-state image sensing element having aphotoelectric conversion element which converts incoming light into anelectrical signal in accordance with an amount of the light, a microlenswhich is arranged on an incident surface, a light guide which isarranged between the photoelectric conversion element and the microlens,and an insulating interlayer which is arranged around the light guide,wherein the solid-state image sensing element located at a distance (H)satisfies:

$\frac{H \cdot D}{L \cdot P} < {{a \cdot \frac{N_{H}}{N_{L}}}\mspace{14mu}{for}\mspace{14mu} 0} < a < 1$where L is a distance from an exit pupil of an image sensing opticalsystem of an image sensing device, which mounts an image sensor formedby two-dimensionally arranging a plurality of the solid-state imagesensing elements, H is a distance from a center of the image sensor to aposition of the solid-state image sensing element on the image sensor, Dis a height from the photoelectric conversion element to an apex of themicrolens, P is a spacing between the plurality of solid-state imagesensing elements, N_(H) is a refractive index of the light guide, andN_(L) is a refractive index of the insulating interlayer.

Further, according to the present invention, a design support method forsupporting to design a solid-state image sensing element having aphotoelectric conversion element which converts incoming light into anelectrical signal in accordance with an amount of the light, a microlenswhich is arranged on an incident surface, a light guide which isarranged between the photoelectric conversion element and the microlens,and an insulating interlayer which is arranged around the light guide,comprises: a condition acquisition step of acquiring at least some ofconditions including a distance L from an exit pupil of an image sensingoptical system of an image sensing device, which mounts an image sensorformed by two-dimensionally arranging a plurality of the solid-stateimage sensing elements, a distance H from a center of the image sensorto a position of the solid-state image sensing element on the imagesensor, a height D from the photoelectric conversion element to an apexof the microlens, a spacing P between the plurality of solid-state imagesensing elements, a refractive index N_(H) of the light guide, and arefractive index N_(L) of the insulating interlayer; a determinationstep of determining if all the conditions can be acquired in thecondition acquisition step; a calculation step of computing, when it isdetermined in the determination step that all the conditions can beacquired,

$\frac{H \cdot D}{L \cdot P} < {a \cdot \frac{N_{H}}{N_{L}}}$and calculating a; a computing step of computing, when it is determinedin the determination step that all the conditions cannot be acquired, avalue which satisfies 0<a<1 for a condition which cannot be acquired;and a notifying step of notifying the calculated a value or the valuecomputed in the computing step.

Further, the foregoing first object is also attained by providing adesign support apparatus for supporting to design a solid-state imagesensing element having a photoelectric conversion element which convertsincoming light into an electrical signal in accordance with an amount ofthe light, a microlens which is arranged on an incident surface, a lightguide which is arranged between the photoelectric conversion element andthe microlens, and an insulating interlayer which is arranged around thelight guide, comprising: a condition acquisition unit that acquires atleast some of conditions including a distance L from an exit pupil of animage sensing optical system of an image sensing device, which mounts animage sensor formed by two-dimensionally arranging a plurality of thesolid-state image sensing elements, a distance H from a center of theimage sensor to a position of the solid-state image sensing element onthe image sensor, a height D from the photoelectric conversion elementto an apex of the microlens, a spacing P between the plurality ofsolid-state image sensing elements, a refractive index N_(H) of thelight guide, and a refractive index N_(L) of the insulating interlayer;a determination unit that determines if all the conditions can beacquired by the condition acquisition unit; a computing unit thatcomputes, when the determination unit determines that all the conditionscan be acquired,

$\frac{H \cdot D}{L \cdot P} < {a \cdot \frac{N_{H}}{N_{L}}}$and calculates a, and that computes, when the determination unitdetermines that all the conditions cannot be acquired, a value whichsatisfies 0<a<1 for a condition which cannot be acquired; and anotifying unit that notifies the calculated a value or the valuecomputed by the computing unit.

Further, the foregoing second object is attained by providing asolid-state image sensing element comprising: a photoelectric conversionelement which converts incoming light into an electrical signal inaccordance with an amount of the light; a microlens which is arranged onan incident surface; a light guide which is arranged between thephotoelectric conversion element and the microlens, and is formed of acomposite material prepared by dispersing in resin one of titanium oxide(TiO₂), silicon nitride (Si₃N₄), and niobium pentoxide (Nb₂O₅); and aninsulating interlayer which is arranged around the light guide and isformed of hydrophobic porous silica, wherein the solid-state imagesensing element located at a distance (H) satisfies:

$\frac{H \cdot D}{L \cdot P} < {{a \cdot \frac{N_{H}}{N_{L}}}\mspace{14mu}{for}\mspace{14mu} 0} < a < 1$where L is a distance from an exit pupil of an image sensing opticalsystem of an image sensing device, which mounts an image sensor formedby two-dimensionally arranging a plurality of the solid-state imagesensing elements, H is a distance from a center of the image sensor to aposition of the solid-state image sensing element on the image sensor, Dis a height from the photoelectric conversion element to an apex of themicrolens, P is a spacing between the plurality of solid-state imagesensing elements, N_(H) is a refractive index of the light guide, andN_(L) is a refractive index of the insulating interlayer.

Further, the foregoing second object is also attained by providing asolid-state image sensing element comprising: a photoelectric conversionelement which converts incoming light into an electrical signal inaccordance with an amount of the light; a microlens which is arranged onan incident surface; a light guide which is arranged between thephotoelectric conversion element and the microlens, and is formed of amaterial selected from silicon nitride (Si₃N₄) and silicon oxynitride(SiON); and an insulating interlayer which is arranged around the lightguide and is formed of silicon oxide (SiO₂), wherein the solid-stateimage sensing element located at a distance (H) satisfies:

$\frac{H \cdot D}{L \cdot P} < {{a \cdot \frac{N_{H}}{N_{L}}}\mspace{14mu}{for}\mspace{14mu} 0} < a < 1$where L is a distance from an exit pupil of an image sensing opticalsystem of an image sensing device, which mounts an image sensor formedby two-dimensionally arranging a plurality of the solid-state imagesensing elements, H is a distance from a center of the image sensor to aposition of the solid-state image sensing element on the image sensor, Dis a height from the photoelectric conversion element to an apex of themicrolens, P is a spacing between the plurality of solid-state imagesensing elements, N_(H) is a refractive index of the light guide, andN_(L) is a refractive index of the insulating interlayer.

Furthermore, the foregoing second object is also attained by providing asolid-state image sensing element comprising: a photoelectric conversionelement which converts incoming light into an electrical signal inaccordance with an amount of the light; a microlens which is arranged onan incident surface; a light guide which is arranged between thephotoelectric conversion element and the microlens, and is formed ofsilicon oxide (SiO₂); and an insulating interlayer which is arrangedaround the light guide and is formed of hydrophobic porous silica,wherein the solid-state image sensing element located at a distance (H)satisfies:

$\frac{H \cdot D}{L \cdot P} < {{a \cdot \frac{N_{H}}{N_{L}}}\mspace{14mu}{for}\mspace{14mu} 0} < a < 1$where L is a distance from an exit pupil of an image sensing opticalsystem of an image sensing device, which mounts an image sensor formedby two-dimensionally arranging a plurality of the solid-state imagesensing elements, H is a distance from a center of the image sensor to aposition of the solid-state image sensing element on the image sensor, Dis a height from the photoelectric conversion element to an apex of themicrolens, P is a spacing between the plurality of solid-state imagesensing elements, N_(H) is a refractive index of the light guide, andN_(L) is a refractive index of the insulating interlayer.

Furthermore, the foregoing third object is attained by providing animage sensing apparatus which has a solid-state image sensing elementhaving a photoelectric conversion element which converts incoming lightinto an electrical signal in accordance with an amount of the light, amicrolens which is arranged on an incident surface, a light guide whichis arranged between the photoelectric conversion element and themicrolens, and an insulating interlayer which is arranged around thelight guide, comprising: an attachment/detachment unit that allows anexchangeable lens to attach/detach to/from the image sensing apparatus,wherein the solid-state image sensing element located at a distance (H)satisfies:

$\frac{H \cdot D}{L \cdot P} < {{a \cdot \frac{N_{H}}{N_{L}}}\mspace{14mu}{for}\mspace{14mu} 0} < a < 1$where L is a distance from an exit pupil of an image sensing opticalsystem of an image sensing device, which mounts an image sensor formedby two-dimensionally arranging a plurality of the solid-state imagesensing elements, H is a distance from a center of the image sensor to aposition of the solid-state image sensing element on the image sensor, Dis a height from the photoelectric conversion element to an apex of themicrolens, P is a spacing between the plurality of solid-state imagesensing elements, N_(H) is a refractive index of the light guide, andN_(L) is a refractive index of the insulating interlayer.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a sectional view showing the concept of an image sensingdevice;

FIG. 2 is an explanatory view showing the positional relationshipbetween an image sensing optical system and image sensor;

FIG. 3 is a sectional view showing the structure of a CMOS typesolid-state image sensing element;

FIG. 4 is a ray-tracing diagram of the solid-state image sensing elementshown in FIG. 3;

FIG. 5 is a ray-tracing diagram of the solid-state image sensing elementshown in FIG. 3;

FIG. 6 is a graph showing the photo-receiving efficiency with respect tothe incident angle of an object light beam onto the solid-state imagesensing element;

FIGS. 7A and 7B are views for explaining the relationship among therefractive index, critical angle, and opening of a light guide;

FIGS. 8A and 8B are views for explaining the relationship between therefractive index and critical angle of a light guide;

FIG. 9 is a graph showing the photo-receiving efficiency with respect tothe incident angle of an object light beam onto the solid-state imagesensing element according to the first embodiment of the presentinvention;

FIG. 10 is a sectional view showing another structure of a CMOS typesolid-state image sensing element;

FIG. 11 is an explanatory view of an incoming light beam when atele-photo lens is mounted on a lens-exchangeable digital camera system;

FIG. 12 is a schematic sectional view of a digital still camera when awide-angle lens is mounted on a lens-exchangeable digital camera system;

FIG. 13 is an explanatory view of an incoming light beam in the digitalcamera system shown in FIG. 12;

FIG. 14 is a side sectional view showing a schematic structure of adigital color camera according to the second embodiment of the presentinvention;

FIG. 15 is a block diagram showing the functional arrangement of thedigital color camera shown in FIG. 14;

FIG. 16 is a view showing the lens arrangement of a zoom lens at thewide-angle end and ray-traces when a stop is open;

FIG. 17 is a view showing the lens arrangement of a zoom lens at thetele-photo end and ray-traces when a stop is open;

FIG. 18 is a view showing the lens arrangement of a zoom lens at thewide-angle end and ray-traces when a stop is stopped down to a pointaperture;

FIG. 19 is a view showing the lens arrangement of a zoom lens at thetele-photo end and ray-traces when a stop is stopped down to a pointaperture;

FIG. 20 is a view showing the lens arrangement of a macro lens andray-traces upon focusing on an object at an infinity;

FIG. 21 is a view showing the lens arrangement of a macro lens andray-traces upon focusing on an object at a near distance;

FIG. 22 is a plan view of an image sensing element according to thesecond embodiment of the present invention;

FIG. 23 is a partial sectional view of the image sensing element;

FIG. 24 is a bird's-eye view of micro convex lenses viewed fromobliquely above;

FIG. 25 is a ray-tracing diagram showing the optical path of incominglight in the image sensing element shown in FIG. 23;

FIG. 26 is a partial sectional view of an image sensing elementaccording to the fourth embodiment of the present invention;

FIG. 27 is a sectional view showing the structure of a CMOS typesolid-state image sensing element;

FIG. 28 is a schematic sectional view showing the structure of aconventional CCD type solid-state image sensing element;

FIG. 29 is a schematic sectional view showing the structure of aconventional CMOS type solid-state image sensing element;

FIG. 30 is a schematic sectional view showing an image sensing system ofa conventional compact digital camera;

FIG. 31 is a schematic sectional view of a conventional digital stillcamera when a tele-photo lens is mounted on a lens-exchangeable digitalcamera system; and

FIG. 32 is a ray-tracing diagram for explaining a limitation on theimage sensing system of the conventional compact digital camera.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail in accordance with the accompanying drawings. However, thedimensions, materials, shapes and relative positions of the constituentparts shown in the embodiments should be changed as convenient dependingon various conditions and on the structure of the apparatus adapted tothe invention, and the invention is not limited to the embodimentsdescribed herein.

<First Embodiment>

FIG. 1 is a sectional view showing the concept of the arrangement of animage sensing device such as a digital still camera system and the like.Referring to FIG. 1, reference numeral 101 denotes a convex lens as animaging optical system; 102, an optical axis of the imaging opticalsystem 101; 103, an image sensor for converting an object light imageformed by the imaging optical system into an electrical signal; and 104,a housing that holds the imaging optical system 101 and image sensor103, and has a function as a camera obscura. Note that the imagingoptical system 101 is illustrated as a single lens (convex lens) for thedescriptive convenience. In practice, the imaging optical system can bean imaging optical system having positive power by combining a pluralityof lenses, reflecting mirrors, or diffraction imaging optical systems.Also, a zoom function may be applied. Furthermore, the imaging opticalsystem 101 may have a stop for light shielding that cuts ghost andflare.

The image sensor 103 comprises a plurality of solid-state image sensingelements. For example, the image sensor 103 is formed by regularly andtwo-dimensionally arranging several million solid-state image sensingelements in the vertical and horizontal directions or oblique directionsso as to obtain image data for several million pixels.

FIG. 2 is an explanatory view showing the positional relationshipbetween the image sensing optical system 101 and image sensor 103.Referring to FIG. 2, the image sensor 103 has a photo-receiving surface105 on which an object light beam focuses via the imaging sensingoptical system 101. Let L be the distance between the imaging sensingoptical system 101 and the photo-receiving surface 105 of the imagesensor 103 in the direction of the optical axis 102 (to be referred toas a “pupil distance” hereinafter), and H be the distance from theoptical axis 102 to the outermost periphery of the photo-receivingsurface 105. Therefore, the distance H corresponds to the image height.Also, let θ be an angle a chief ray 107 makes with the optical axis 102,the chief ray 107 emerging from an intersection between the optical axis102 and an exit pupil 106 of the image sensing optical system 101.

FIG. 3 is a sectional view showing an example of an image sensorequipped in an image sensing device such as a digital still camerasystem or the like, i.e., solid-state image sensing elements 200 for twopixels of a CMOS type image sensor having a light guide in a portion Aof the image sensor 103 shown in FIG. 2.

Referring to FIG. 3, reference numeral 201 denotes a photoelectricconversion unit; 202, a silicon (Si) substrate on which thephotoelectric conversion unit 201 is formed; and 203, a light guideformed of SiN or the like as a material having a high refractive index.The central axis of the light guide 203 substantially agrees with thatof the photoelectric conversion unit 201. The light entrance side of thelight guide 203 is formed to have a broader opening so as to receivemore light components. Reference numeral 210 denotes a transferelectrode which is formed in an insulating interlayer 211 formed of SiO₂or the like with a low refractive index, and is used to transfer a photocharge generated by the photoelectric conversion unit 201 to a floatingdiffusion (FD) unit (not shown); and 204, wiring electrodes having alight-shielding function of preventing light from entering portionsother than the photoelectric conversion unit 201. Reference numeral 206denotes a flattening layer which is formed on a uneven surface due toelectrodes and wiring layers (not shown) to provide a flat surface. Acolor filter 207 is formed on the flattening layer 206, and a microlens209 is also formed on the flattening layer 206. The shape and layoutposition of the microlens 209 are determined to focus an object lightbeam coming from the image sensing optical system 101 shown in FIG. 2onto the photoelectric conversion unit 201.

Light transmitted through the microlens 209 is transmitted through theflattening layer 208, and undergoes wavelength selection in the colorfilter layer 207. For example, when the color filter layer 207 of theleft pixel in FIG. 3 transmits a green light component, blue and redlight components are absorbed. When the color filter layer 207 of theright pixel in FIG. 3 transmits a blue light component, green and redlight components are absorbed. Light of a predetermined wavelength,which has been transmitted through the color filter layer 207 istransmitted through the light guide 203 formed of a transparent materialwith a high refractive index (refractive index N_(H)) such as siliconnitride (SiN) or the like, and is guided to the photoelectric conversionunit 201. Since the insulating interlayer 211 is formed around the lightguide 203 using a transparent material with a low refractive index(refractive index N_(L)) such as silicon oxide (SiO₂) or the like, lightthat goes from the light guide 203 to the insulating interlayer 211 istotally reflected by a boundary surface between the light guide 203 andinsulating interlayer 211, and is guided to the photoelectric conversionunit 201. The refractive index N_(L) of the insulating interlayer 211formed of silicon oxide (SiO₂) is, e.g., 1.46.

Let P be the spacing (pixel pitch) between neighboring pixels, and D bethe height from the apex of the microlens 209 to the photo-receivingsurface of the photoelectric conversion unit 201.

FIG. 4 is a ray-tracing diagram in the pixel arrangement shown in FIG. 3when the image sensing optical system 101 is “close” to the image sensor103, i.e., the pupil distance L is short, and FIG. 5 is a ray-tracingdiagram in the pixel arrangement shown in FIG. 3 when the image sensingoptical system 101 is “far” from the image sensor 103, i.e., the pupildistance L is long.

In case of the solid-state image sensing element 200 with the lightguide 203, as shown in FIG. 4, even when the indent angle θ=α1 of anobject light beam 330 with respect to an optical axis 321 is large (whenthe pupil distance L is short), the light is totally reflected by aslope of the light guide 203, and is efficiently guided to thephotoelectric conversion unit 201.

When the pupil distance L of the image sensing optical system 101 islong and the indent angle θ=α2 of the object light beam 330 with respectto the optical axis 321 is small, as shown in FIG. 5, the object light330 directly enters the photoelectric conversion unit 201 without beingreflected by the slope of the light guide 203.

FIG. 6 is a graph showing the photo-receiving efficiency of thesolid-state image sensing element 200 with the structure shown in FIG. 3with respect to the incident angle of the object light beam. Note thatthe dotted curve in FIG. 6 shows the photo-receiving efficiency of asolid-state image sensing element without any light guide 203 forreference. The graph shown in FIG. 6 shows the ratio of thephoto-receiving amount of the photoelectric conversion unit 201 withrespect to the incident angle θ of the object light beam 330, so as tohave “1” as a case wherein the amount of the object light beam 330received by the photoelectric conversion unit 201 via the microlens 209becomes maximum when the angle (incident angle) θ the object light beammakes with the central axis 321 of the microlens 209 (or the centralaxis of the photoelectric conversion unit 201) is changed. In FIG. 6,the ordinate plots the ratio of the photo-receiving amount, and theabscissa plots the incident angle θ. Also, in FIG. 6, assume that theobject light beam 330 is parallel light, and a pixel is located at theoutermost periphery of the image sensor 103.

For example, if the incident angle range when the ratio of thephoto-receiving amount is “0.8” or more is determined as an effectiverange (a range in which an object image can be reproduced with highdefinition) of the solid-state image sensing element, when no lightguide 203 is formed, allowance of an incident angle of the object lightbeam ranges for about 17. On the other hand, when the light guide 203 isformed, allowance of an incident angle of the object light beam rangesfor about 24°.

The incident angle range of the object light beam within which apredetermined photo-receiving ratio can be obtained is called “incidentangle redundancy”. In the example shown in FIG. 6, an incident angleredundancy θ₂ when the light guide 203 is formed is about 24, and anincident angle redundancy θ₁ when no light guide 203 is formed is about17°. Hence, we can say that “the incident angle redundancy is improvedby about 7°” when the light guide 203 is formed compared to the casewherein no light guide 203 is formed.

When the image sensing optical system 101 performs zooming, the angle ofthe chief ray (an oblique ray that has passed the center of the pupil106 of the image sensing optical system 101 of the object light beam) ofthe object light beam that enters the solid-state image sensing element200 changes in accordance with the pupil position of the image sensingoptical system 101 that changes according to the focal length (see θ inFIG. 2). Hence, the “incident angle redundancy” can be rephrased as anallowable range of the angle of the chief ray or an allowable range ofthe pupil position. The allowable range of the pupil position will bereferred to as a “redundancy of the pupil position” or “pupilredundancy”.

The relationship between the solid-state image sensing element 200 andpupil redundancy in the first embodiment will be described below.

As shown in FIG. 2, since the angle the chief ray 107 makes with theoptical axis 102 is θ, we have:

$\begin{matrix}{{\tan\;\theta} = \frac{H}{L}} & (1)\end{matrix}$Based on this, the relationship among the image height H, pupil distanceL, pixel pitch P, height D, refractive index N_(H) of the light guide203, and refractive index N_(L) of the insulating interlayer 211 isgiven by:

$\begin{matrix}{\frac{H \cdot D}{L \cdot P} < {a \cdot \frac{N_{H}}{N_{L}}}} & (2)\end{matrix}$When the image height H, pupil distance L, pixel pitch P, height D,refractive index N_(H) of the light guide, and refractive index N_(L) ofthe insulating interlayer are selected to make the coefficient a meet:0<a<1  (3)the effect for the photo-receiving efficiency of the light guidesstructure can be improved.

Inequality (2) will be described in detail below.

FIGS. 7A and 7B are views for explaining the relationship between therefractive index of the light guide 203 and the critical angle thatcauses total reflection by the slope of the light guide 203, and simplyillustrate only portions associated with a description of the structureof the solid-state image sensing element 200 shown in FIG. 3.

The refractive index N_(H) of the light guide 203 is n₁ in FIG. 7A, andit is n₂ in FIG. 7B (n₁<n₂). As shown in FIGS. 7A and 7B, if therefractive index N_(H) of the light guide 203 becomes large (n₁<n₂), acritical angle β that causes total reflection by the slope of the lightguide 203 becomes small (β₁<β₂). Hence, the opening on the lightentrance side of the light guide 203 can be broadened.

As shown in FIGS. 8A and 8B, if the shape of the light guide 203 remainsthe same, the critical angle β becomes larger (β₁<β₂) when therefractive index N_(H) is large (n₁<n₂), as described above. Hence, witha larger reference index N_(H), the object light beam 330 with a largerincident angle θ when the pupil distance L is short and the angle θ theoptical axis 102 makes with the chief ray 107 in FIG. 2 is larger can betotally reflected by the slope of the light guide 203, and can beefficiently guided to the photoelectric conversion unit 201 (θ₁<θ₂),thus improving the pupil redundancy.

Furthermore, the same applies to a case wherein the refractive indexN_(L) of the insulating interlayer 211 is decreased. That is, since thecritical angle β that causes total reflection by the slope of the lightguide 203 becomes small in this case, the pupil redundancy can beimproved as in the case of large N_(H). Also, the opening can bebroadened.

That is, as can be seen from FIG. 2, when the image height H is constantand the pupil distance L becomes short, the angle θ the optical axis 102makes with the chief ray 107 increases with decreasing pupil distance L.Hence, by increasing the refractive index N_(H) of the light guide 203or decreasing the refractive index N_(L) of the insulating interlayer211 accordingly, the pupil redundancy can be improved. Also, the openingcan be broadened.

The same applies to a case wherein the pupil distance L is constant andthe image height H increases. As can be seen from FIG. 2, since theangle θ the optical axis 102 makes with the chief ray 107 increases withincreasing image height H, the pupil redundancy can be improved byincreasing the refractive index N_(H) of the light guide 203 ordecreasing the refractive index N_(L) of the insulating interlayer 211accordingly. Also, the opening can be broadened.

Moreover, even when the image height H and pupil distance L areconstant, if the height D of the solid-state image sensing element 200shown in FIG. 3 increases, the incident angle of the object light beam330 becomes deeper. In such case as well, by increasing the refractiveindex N_(H) of the light guide 203 or decreasing the refractive indexN_(L) of the insulating interlayer 211 according to an increase inheight D of the solid-state image sensing element 200, the pupilredundancy can be improved. Also, the opening can be broadened.

In addition, when the image height H and pupil distance L are constant,if the pixel pitch P of the solid-state image sensing element 200 isnarrowed down, the size of the photoelectric conversion unit 201decreases (i.e., a pixel size is reduced) because of wiring layers andthe like, and the object light beam 330 that enters the photoelectricconversion unit 201 decreases. In order to increase the amount of theobject light beam 330 that enters the photoelectric conversion unit 201without changing the size of the photoelectric conversion unit 201, therefractive index N_(H) of the light guide 203 is increased or therefractive index N_(L) of the insulating interlayer 211 is decreasedwith decreasing pixel pitch P of the solid-state image sensing element200. As a result, a broader incident angle redundancy can be assured.Hence, even when the slope of the side surface of the light guide 203 isincreased to broaden the opening, as shown in FIG. 7B, the object lightbeam 330 that enters the photoelectric conversion unit 201 can beincreased.

The coefficient a in the right-hand side of inequality (2) will bedescribed below.

FIG. 9 is a graph showing the photo-receiving efficiency of thesolid-state image sensing element 200 with respect to the incident angleof the object light beam in one pixel located at the center of thesolid-state image sensing element 200. As in FIG. 6, FIG. 9 shows theratio of the photo-receiving amount of the photoelectric conversion unit201 with respect to the incident angle θ of the object light beam 330,so as to have “1” as a case wherein the amount of the object light beam330 received by the photoelectric conversion unit 201 via the microlens209 becomes maximum when the angle (incident angle) θ the object lightbeam makes with the central axis 321 of the microlens 209 (or thecentral axis of the photoelectric conversion unit 201) is changed. Also,assume that the object light beam 330 is parallel light.

The theoretical limit shown in FIG. 9 indicates the cosine-4^(th)-powerlaw. The cosine-4^(th)-power law will be briefly described below byapplying it to the solid-state image sensing element 200. If the amountof the object light beam 330 is constant, the amount of light receivedby the photoelectric conversion unit 201 is proportional to the 4thpower of cosine of the angle θ the chief ray 107 makes with the opticalaxis 102. Hence, the amount of light that enters the photoelectricconversion unit 201 decreases in accordance with the incident angle ofthe object light beam 330.

Note that theoretically the cosine-4^(th)-power law can be applied toonly the central pixel of the solid-state image sensing element 200.However, a peripheral pixel exhibits the same tendency as the centralpixel although its peak position deviates.

Also, FIG. 9 shows simulation results when the refractive index N_(H) ofthe light guide 203 is 1.65 and 1.80. At this time, the values such asthe height D of the solid-state image sensing element 200 are asfollows:

-   -   image height H=4251 [μm]    -   pupil distance L=15000 [μm]    -   pixel pitch P=3.25 [μm]    -   height D=6.0 [μm]    -   refractive index N_(L) of insulating interlayer 211=1.46

When the aforementioned values are substituted in inequality (2) and theposition of the radio=“0.8” of the light amount of the solid-state imagesensing element 200 is defined as the effective range (as the definitionrange of the pupil redundancy), the calculated coefficient a is:a=0.717  (4)This a satisfies inequality (3).

In case of the conventional compact digital camera shown in FIG. 30, theimage height H=3320 μm and the incident angle θ of the chief ray 107falls within the range from 3 to 9, as described above. At this time,assume that the pupil distance L ranges from 21 mm to 60 mm.

For example, assuming the solid-state image sensing element 200 whichsatisfies the pupil distance L=7 mm to 20 mm as ⅓ of the conventionalvalues, the relationship between the pixel pitch P of the solid-stateimage sensing element 200 and the refractive index N_(H) of the lightguide 203 is calculated based on inequality (2) and equation (4) by:N_(H)×P>5.795 [μm]Since the resolution improves with decreasing pixel pitch P of thesolid-state image sensing element 200, if the pixel pitch P is 3.25 μm,we have:N_(H)>1.78  (5)

Hence, by forming the light guide 203 of the solid-state image sensingelement 200 equipped in the compact digital camera using a material thatsatisfies inequality (5), light transmitted through the light guide 203is totally reflected by the boundary surface between the light guide andthe insulating interlayer 211, and is efficiently collected on thephotoelectric conversion unit. As a result, a high-quality image can beobtained, and a high-resolution image can also be obtained since asolid-state image sensing element with a smaller pixel size can beadopted. Furthermore, since the pupil distance L can be shortened, lightcan be efficiently collected on the photoelectric conversion unit 201 incase of a tele-photo type image sensing optical system 101 which cannotbe adopted in the conventional compact digital camera. Hence, not onlythe degree of freedom in design of the image sensing system improves,but also a size reduction of the image sensing system can be achieved.In the above example, the refractive index N_(H) of the light guide 203is calculated. However, the present invention is not limited to this,and any of conditions in inequality (2) may be open. In this manner, anunsettled condition can be simulated based on values settled as designconditions.

As described above, a program that computes inequality (2) is input inadvance to an information processing apparatus such as a personalcomputer or the like, computes using input parameters that indicaterequired conditions, and displays the determination result andcomputation result of equation (4) and inequality (5). Thus, thedesigner can easily know if the solid-state image sensing element thatmeets the input conditions has a sufficient critical angle, or whichcondition is to be satisfied to realize a solid-state image sensingelement that meets the conditions (dimensions, material, and the like),thus allowing easy design of the solid-state image sensing element.

The structure of the solid-state image sensing element that can beapplied to the present invention is not limited to that shown in FIG. 3.FIG. 10 shows another example of the structure of a solid-state imagesensing element which can be applied to the present invention.

The same reference numerals in FIG. 10 denote the same parts as in FIG.3. FIG. 10 shows an example having a second wiring electrode 717 whichhas a light shielding function of preventing light from enteringportions other than the photoelectric conversion unit 201, in additionto components shown in FIG. 3. The flattening layer 206 is formed on anuneven surface due to the second wiring electrode 717 and wiring layers(not shown) to provide a flat surface.

To summarize the aforementioned contents, in order to improve the lightcollecting effect even in case of an object light beam which has a largeincident angle to the solid-state image sensing element 200, thestructure of the light guide is determined based on the followingproperties.

1. If the image height H increases, the incident angle θ becomes larger.

2. If the pupil distance L increases, the incident angle θ becomessmaller.

3. The critical angle that causes total reflection at the boundarysurface between the light guide and the insulating interlayer decreaseswith decreasing N_(L)/N_(H), i.e., the ratio of the refractive indexN_(L) of the insulating interlayer to the refractive index N_(H) of thelight guide, and light rays incident at a larger incident angle θ can becaptured.

4. If the pixel pitch P decreases, an area occupied by a circuit portionof each pixel increases, the photoelectric conversion unit sizedecreases relatively, and light rays incident at a larger incident angleθ cannot be captured. In case of the CMOS type solid-state image sensingelement, the circuit portion includes a charge transfer MOS transistor,a reset MOS transfer for supplying a reset potential, a source-followerMOS sensor transistor, a selection MOS transistor for selectivelyoutputting a signal from the source-follower MOS sensor transistor, andthe like.

5. If the height D from the photoelectric conversion unit to themicrolens increases, an angle at which the photoelectric conversion unitcan be seen from the microlens decreases, and light rays with a largerincident angle θ cannot be captured.

As can be seen from these properties, an evaluation value E, which isbased on inequality (2) expressed by the image height H, pupil distanceL, pixel pitch P, height D, refractive index N_(H) of the light guide,and refractive index N_(L) of the insulating interlayer, and is givenby:

$\begin{matrix}{E = \frac{H \cdot D \cdot N_{L}}{L \cdot P \cdot N_{H}}} & (6)\end{matrix}$can be an index suited to express the amount of light rays with largeincident angle θ that can be guided to the photoelectric conversionunit. Note that the effect of the light guide structure is large whenthe image height H, pupil distance L, pixel pitch P, height D,refractive index N_(H) of the light guide, and refractive index N_(L) ofthe insulating interlayer are selected to meet:E<1.0  (7)

It is ideal that the lens-exchangeable digital camera system uses asolid-state image sensing element having a light guide that canefficiently focus object light independently of an exchangeable lensmounted on the camera body. The light guide is formed based oninequality (2) using lens information of an exchangeable lens that canbe mounted on the camera.

FIG. 11 is an explanatory view of an incoming light beam to an imagesensor 1208 when the image sensor using the solid-state image sensingelements with the above structure is applied to a lens-exchangeabledigital camera system shown in FIG. 31. As described above, in FIG. 31,a tele-photo lens 1220 is mounted as an exchangeable lens.

In the lens-exchangeable digital camera system shown in FIG. 31, theframe size of the image sensor 1208 to be mounted is substantially equalto the APS-C size (about 17×25 mm) as the film size of a silver halidecamera. Hence, the image height H of pixels located at corners of theframe is about 15 mm.

Also, the height D from the apex of the microlens to the photoelectricconversion unit of the solid-state image sensing element used in theimage sensor 1208 is about 0.006 mm.

The insulating interlayer filled around the light guide formed in theimage sensor 1208 normally uses silicon oxide (SiO₂), and its refractiveindex N_(L) is 1.46. Also, the light guide is normally formed of siliconnitride (SiN), and its refractive index N_(H) is 2.0. Note that siliconoxide and silicon nitride are merely an example, and the presentinvention is not limited to these specific materials.

FIG. 11 indicates the position of an exit pupil 1225 of the tele-photolens 1220. The exit pupil 1225 is formed at the position of a distanceL_(t) farther from the image sensor 1208. An object light beam that hasbeen transmitted through the exit pupil 1225 enters the sensor 1208 atthe position of the image height H. At this time, an incident angleθ_(t) of a chief ray to the image sensor 1208 satisfies:tan θ_(t) =H/L _(t)

FIG. 12 is a schematic view when the image sensor including thesolid-state image sensing elements with the above structure is appliedto a lens-exchangeable camera system on which a wide-angle lens 420 ismounted. Since the structure of the camera body is the same as thatshown in FIG. 31, the same reference numerals denote its components, anda description thereof will be omitted.

A camera body 1200 and wide-angle lens 420 are coupled via a camera-sidemount 1211 and lens-side mount 421. An electrical circuit such as a lensMPU, lens memory, and the like (not shown) provided to the wide-anglelens 420 is coupled to an electrical circuit such as a camera MPU andthe like (not shown) via a lens-side contact 422 and camera-side contact1212. The lens memory stores lens information such as the exit pupilposition of the exchangeable lens and the like.

FIG. 13 is an explanatory view of an incoming light beam to the imagesensor 1208 arranged in the digital camera system on which thewide-angle lens 420 shown in FIG. 12 is mounted. In FIG. 13, an exitpupil 425 of the retrofocus type wide-angle lens 420 is formed at theposition of a distance L_(w) closer to the image sensor 1208 than whenthe tele-photo lens 1220 is mounted (FIG. 11). An object light beam thathas been transmitted through the exit pupil 425 of the wide-angle lens420 enters the image sensor 1208 at the position of the image height H.At this time, an incident angle θ_(w) of a chief ray to the image sensor1208 satisfies:tan θ_(w) =H/L _(w)

As can be seen from FIGS. 11 and 13, the chief ray angle θ_(w) when thewide-angle lens is mounted on the camera and the chief ray angle θ_(t)when the tele-photo lens is mounted meet:θ_(w)>θ_(t)and the incident angle θ of the chief ray to the image sensor 1208 islarger when the wide-angle lens is mounted. Therefore, by determiningthe structure of the light guide using the exit pupil distance of a lenshaving a shorter exit pupil distance from the image height ofexchangeable lenses that can be mounted on the camera, a solid-stateimage sensing element with higher photo-receiving efficiency can bedesigned. If the exit pupil distance L of a lens having a shorter exitpupil distance from the image height of the exchangeable lenses that canbe mounted on the camera is about 60 mm (other conditions are the sameas those described above), the relationship between the pixel pitch P ofthe image sensor 1208 and the evaluation value E is calculated based oninequality (2) by:E×P=0.0011 [mm]Since the resolution improves with decreasing pixel pitch P of the imagesensor 1208, if the pixel pitch P is set to be 0.003 mm, the evaluationvalue E is:E=0.37which satisfies inequality (7).

In this way, when the light guide of the solid-state image sensingelement 200 to be mounted on the lens-exchangeable digital camera systemis formed to satisfy equation (6) and inequality (7) using exchangeablelens information, light transmitted through the light guide is totallyreflected by the boundary surface between the light guide and theinsulating interlayer and is efficiently collected on the photoelectricconversion unit. As a result, a high-quality image can be obtained, anda high-resolution image can also be obtained since a solid-state imagesensing element with a smaller pixel size can be adopted.

In the first embodiment, the structure of the light guide formed in thesolid-state image sensing element is determined based on the exit pupilinformation of an exchangeable lens that can be mounted on the camera.Also, it is effective to determine the structure of the light guide inconsideration of an open F-value in addition to the exit pupilinformation of an exchangeable lens.

As described above, when the light guide of the solid-state imagesensing element to be mounted on an optical device is formed using amaterial that satisfies inequalities (2) and (3) irrespective of thecompact digital camera or lens-exchangeable digital still camera, lighttransmitted through the light guide is totally reflected by the boundarysurface between the light guide and the insulating interlayer, and isefficiently collected on the photoelectric conversion unit. As a result,a high-quality image can be obtained, and a high-resolution image canalso be obtained since a solid-state image sensing element with asmaller pixel size can be adopted.

In case of the compact digital camera, the degree of freedom in designof the image sensing system improves, and a size reduction of the imagesensing system can be achieved.

<Second Embodiment>

FIG. 14 is a side sectional view showing a schematic structure of adigital color camera as an image sensing device according to the secondembodiment of the present invention. This camera is a single-plate typedigital color camera using an image sensing element such as a CCD, CMOSsensor, or the like, and obtains an image signal indicating a moving orstill image by driving the image sensing element continuously or in aone-shot manner. Note that the image sensing element is an area sensorwhich converts incoming light into charges according to the amount oflight, accumulates the charges for respective pixels, and reads out theaccumulated charges.

Referring to FIG. 14, reference numeral 110 denotes a camera body; and126, a lens device which includes an image sensing lens 125 and isdetachable from the camera body 110. Note that FIG. 14 depicts only onelens as the image sensing lens 125. However, the image sensing lens 125is normally formed by combining a plurality of lenses. The lens device126 is electrically and mechanically connected to the camera body 110via a known mount mechanism. By exchanging lens devices having differentfocal lengths, images with various angle of view can be shot. The lensdevice 126 includes a drive mechanism (not shown), which moves afocusing lens as an element of the image sensing lens in the directionof an optical axis L1, or change a refracting power to change theboundary surface shape when the focusing lens is formed of a flexibletransparent elastic member or liquid lens, thereby attains focusadjustment to an object.

Reference numeral 116 denotes an image sensing element housed in apackage 124. An optical low-pass filter 156 that controls the spatialfrequency characteristics of the image sensing lens 125 is inserted inan optical path extending from the image sensing lens 125 to the imagesensing element 116, so as not to transmit unnecessarily high spatialfrequency components of an object image to the image sensing element116. Also, an infrared cut filter (not shown) is formed on the imagesensing lens 125.

An object image captured by the image sensing element 116 is displayedon a display device 117. The display device 117 is attached to the backsurface of the camera, and the user can directly observe the displayedimage. The display device 117 can be formed as a low-profile structurehaving low power consumption, when it comprises an organic EL spatialmodulation element or liquid crystal spatial modulation element, aspatial modulation element that utilizes electrophoretic migration offine particles, or the like. Hence, such display device is convenientfor a portable device.

Assume that the image sensing element 116 is a CMOS process compatiblesensor which is one of amplification type image sensing elements in thisembodiment. As one feature of the CMOS image sensing element, sinceperipheral circuits such as an image sensing element drive circuit, A/Dconversion circuit, and image processor can be formed in the sameprocess as MOS transistors of an area sensor portion, the numbers ofmasks and processes can be greatly reduced compared to the CCD. Also,the CMOS image sensing element has a feature that allows random accessto an arbitrary pixel, and can read out pixel outputs by decimating themfor display, thus allowing real-time display at a high display rate. Theimage sensing element 116 performs a display image output operation andhigh-definition image output operation by utilizing these features. Notethat the present invention is not limited to the CMOS sensor, andsolid-state image sensing elements of other types such as a CCD and thelike can be used.

Reference numeral 111 denotes a movable half mirror which splits theoptical path from the image sensing lens 125 to an optical viewfinder;115, a focusing screen arranged on a prospective image field of anobject image; and 112, a pentaprism. Reference numeral 118 denotes alens used to observe a viewfinder image. The lens 118 includes aplurality of lenses for the dioptric adjustment function in practice.The focusing screen 115, pentaprism 112, and lens 118 form a viewfinderoptical system. The refractive index of the half mirror 111 is about1.5, and its thickness is 0.5 mm. A movable sub mirror 122 is arrangedbehind the half mirror 111, and deflects, to a focus detection unit 121,a light beam closer to the optical axis of that which has beentransmitted through the half mirror 111. The sub mirror 122 rotatesabout a rotation axis (not shown) and retracts from an image sensingoptical path together with the half mirror 111 upon image sensing. Thefocus detection unit 121 attains focus detection based on, e.g., a phasedifference detection method.

A small pyramidal periodic structure having a pitch smaller than thewavelength of visible light is formed using a resin on the surface ofthe half mirror 111 to serve as so-called photonic crystals, therebyreducing surface reflection of light due to the refractive indexdifference between air and the resin, and improving the light useefficiency. With this structure, any ghost produced by multiplereflection of light by the back and front surfaces of the half mirrorcan be suppressed.

A mirror drive mechanism which includes an electromagnetic motor andgear train (not shown) switches a state wherein it changes the positionsof the half mirror 111 and sub mirror 122 to make a light beam from theimage sensing lens 125 directly strike the image sensing element 116,and a state wherein the optical path is split to the optical viewfinder.

Reference numeral 114 denotes a movable flash emission device; 113, afocal plane shutter; 119, a main switch; 120, a release button; 123, aviewfinder mode switch for switching between the optical viewfinder andelectronic viewfinder; and 180, an optical viewfinder informationdisplay unit.

FIG. 15 is a block diagram showing the functional arrangement of theaforementioned digital color camera. Note that the same referencenumerals in FIG. 15 denote the same parts as in FIG. 14.

The camera has an image sensing system, image processing system,recording/reproduction system, and control system. The image sensingsystem includes the image sensing lens 125 and image sensing element116. The image processing system includes an A/D converter 130, RGBimage processor 131, and YC processor 132. The recording/reproductionsystem includes a recording processor 133 and reproduction processor134. The control system includes a camera system controller 135, anoperation detector 136, and a drive circuit 137 for the image sensingelement 116. Reference numeral 138 denotes a standardized connectionterminal used to connect an external computer or the like so as toexchange data. These components are driven by a power supply means (notshown) such as a primary battery (alkaline battery, lithium battery, orthe like), a secondary battery (NiCd battery, NiMH battery, Li battery,or the like), a compact fuel battery, an AC adapter, or the like.

The image sensing system is an optical processing system which imageslight coming from an object on the image sensing surface of the imagesensing element 116 via the image sensing lens 125, and exposes theimage sensing element 116 with an appropriate amount of object light byadjusting a stop (not shown) of the lens device 126 and also the focalplane shutter 113 as needed. The image sensing element 116 has a totalof about 40 million square pixels (7400 in the longitudinaldirection×5600 in the widthwise direction), and arranges one of R (red),G (green), and B color filters on every four pixels as one set in aso-called Bayer arrangement. In the Bayer arrangement, G pixels whichare felt intensively when the observer observes an image are arrangedmore than R and B pixels, thus improving the total image quality. Ingeneral, an image process using the image sensing element of this typegenerates most of a luminance signal from a G signal, and generatescolor signals from R, G, and B signals. Note that the number of pixelsand the color filter arrangement are not limited to the aforementionedones, and can be changed as needed.

An image signal read out from the image sensing element 116 is suppliedto the image processing system via the A/D converter 130. The A/Dconverter 130 is a signal processing circuit which converts into andoutputs a 12-bit digital signal according to the amplitude of a signalof each exposed pixel. The image signal process after the A/D converter130 is executed as a digital process.

The image processing system is a signal processing circuit which obtainsan image signal of a desired format from the R, G, and B digitalsignals, and converts R, G, and B signals into YC signals including aluminance signal Y and color difference signals (R-Y) and (B-Y), or thelike.

The RGB image processor 131 is a signal processing circuit forprocessing image signals of 7400×5600 pixels received from the imagesensing element 116 via the A/D converter 130, and has a white balancecircuit, gamma correction circuit, and interpolation circuit thatattains high-resolution conversion by interpolation.

The YC processor 132 is a signal processing circuit for generating aluminance signal Y and color difference signals R-Y and B-Y. The YCprocessor 132 includes a high frequency luminance signal generationcircuit for generating a high frequency luminance signal YH, a lowfrequency luminance signal generation circuit for generating a lowfrequency luminance signal YL, and a color difference signal generationcircuit for generating the color difference signals R-Y and B-Y. Theluminance signal Y is formed by mixing the high and low frequencyluminance signals YH and YL.

The recording/reproduction system is a processing system which outputsan image signal to a memory (not shown) and outputs an image signal tothe display device 117. The recording processor 133 performs read andwrite processes of an image signal on the memory, and the reproductionprocessor 134 reproduces an image signal read out from the memory, andoutputs it to the display device 117.

The recording processor 133 includes a compression/expansion circuitwhich compresses YC signals that represents a still image or movingimage in a predetermined compression format, and expands the compresseddata when it is read out. The compression/expansion circuit includes aframe memory for a signal process, stores the YC signals from the imageprocessing system for each frame in the frame memory reads out the YCsignals for a plurality of blocks, and applies compression encoding tothem. The compression encoding is done by applying two-dimensionalorthogonal transformation, normalization, and Huffman encoding to imagesignals for respective blocks.

The reproduction processor 134 is a circuit for applying matrixconversion to the luminance signal Y and color difference signals R-Yand B-Y into, e.g., RGB signals. The signal converted by thereproduction processor 134 is output to the display device 117 toreproduce and display a visible image. The reproduction processor 134and display device 117 may be connected via a wireless communicationmeans such as Bluetooth or the like. With this arrangement, an imageshot by this digital color camera can be monitored from a remote place.

The control system includes the operation detector 136 which detectsoperations of the release button 120, viewfinder mode switch 123, andthe like, the camera system controller 135 which controls respectiveunits including the half mirror 111 and sub mirror 122 in response tothe detection signal from the operation detector 136, and generates andoutputs timing signals and the like upon image sensing, the drivecircuit 137 for generating a drive signal for driving the image sensingelement 116 under the control of the camera system controller 135, andan information display unit 142 for controlling the optical viewfinderinformation display device 180.

The control system controls the image sensing system, image processingsystem, and recording/reproduction system in response to externaloperations. For example, the control system controls the drive operationof the image sensing element 116, the operation of the RGB imageprocessor 131, the compression process of the recording processor 133,and the like upon detection of depression of the release button 120.Furthermore, the control system controls the states of respectivesegments of the optical viewfinder information display device 180 thatdisplays information in the optical viewfinder using the informationdisplay unit 142.

The camera system controller 135 checks the luminance level of an objecton the basis of the luminance signal Y obtained from the YC processor132. If it is determined that the object luminance level is low, andsufficient focus detection precision cannot be assured, the controller135 instructs the flash emission device 114 or a white LED, fluorescenttube, or the like to illuminate an object with light. Conversely, if itis determined that the object luminance level is too high to causehighlight saturation, the controller 135 increases the shutter speed ofthe focal plane shutter 113 or shortens the charge accumulation periodof the image sensing element 116 by an electronic shutter. In this way,the controller 135 adjusts an exposure amount.

An AF controller 140 and lens system controller 141 are furtherconnected to the camera system controller 135. These controllersexchange data required for processes via the camera system controller135.

The AF controller 140 obtains a signal output from a focus detectionsensor 167 in a focus detection area set at a predetermined position onthe image sensing frame, generates a focus detection signal on the basisof this signal output, and detects the fucusing state of the imagesensing lens 125. Upon detection of defocus, the AF controller 140converts this amount into the drive amount of the focusing lens as anelement of the image sensing lens 125, and transmits it to the lenssystem controller 141 via the camera system controller 135. For a movingobject, the AF controller 140 instructs the drive amount of the focusinglens on the basis of an estimation result of an appropriate lensposition in consideration of a time lag from when the release button 120is pressed until actual image sensing control starts.

Upon reception of the drive amount of the focusing lens, the lens systemcontroller 141 performs, e.g., an operation for moving the focusing lensin the direction of the optical axis L1 using a drive mechanism (notshown) in the lens device 126, thus adjusting a focus on an object. Whenthe AF controller 140 detects that a focus is adjusted onto the object,this information is supplied to the camera system controller 135. Atthis time, if the release button 120 is pressed, the image sensingcontrol is implemented by the image sensing system, image processingsystem, and recording/reproduction system, as described above.

FIGS. 16 and 17 are views showing the arrangement of a zoom lens as oneof image sensing lenses assembled in the lens device 126. FIGS. 16 and17 exemplify a tele-photo zoom lens with a 5-group arrangement(positive, negative, positive, positive, and negative groups). Theselens groups will be referred to as first to fifth groups ZG1 to ZG5 inturn from the object side. FIG. 16 shows the state at the wide-angleend, and FIG. 17 shows the state at the tele-photo end. FIGS. 16 and 17show ray-traces in an aperture open state. Assume that the focal lengthand f-number at the wide-angle end are 100 mm and 5.6, and those at thetele-photo end are 400 mm and 8.0.

As shown in FIGS. 16 and 17, the first group ZG1 includes a positivelens 511 having a convex surface facing the object side, a negativemeniscus lens 512 having a convex surface facing the object side, and apositive lens 513 which is cemented to the negative meniscus lens 512and has a surface with a stronger curvature facing the object side. Thesecond group ZG2 includes a double-concave negative lens 521, and apositive lens 522 having a surface with a stronger curvature facing theobject side. The third group ZG3 includes a positive lens 531 having aconvex surface facing the image side. The fourth group ZG4 includes adouble-convex positive lens 541, and a negative lens 542 which iscemented to the positive lens 541 and has a concave surface facing theobject side. The fifth group ZG5 includes a positive lens 551 having asurface with a stronger curvature facing the image side, and adouble-concave negative lens 552 which is cemented to the positive lens551. A stop ZS is inserted between the second and third groups ZG2 andZG3.

Upon zooming from the wide-angle end to the tele-photo end, the airspace between the second and third groups ZG2 and ZG3 contracts whilethat between the first and second groups ZG1 and ZG2 expands.Furthermore, the air space between the fourth and fifth groups ZG4 andZG5 contracts while that between the third and fourth groups ZG3 and ZG4expands. More specifically, the first group ZG1 moves toward the objectside, the second group ZG2 moves toward the image side, the third groupZG3 moves toward the object side, and the fifth group ZG5 moves towardthe object side, while the fourth group ZG4 is fixed at a position withrespect to an image sensing surface 501.

Since the exit pupil position varies upon zooming, the incident angle ofa light ray that strikes the off-axis image sensing position changesaccording to the set focal length. An angle θ₁ shown in FIG. 16 is anincident angle when a light beam that strikes a maximum-angle-of-viewposition at the wide-angle end is represented by its light amountbarycenter. An angle θ₂ shown in FIG. 17 is an incident angle when alight beam that strikes a maximum-angle-of-view position at thetele-photo end is represented by its light amount barycenter. Since theexit pupil position becomes closer to the image sensing surface at thewide-angle end, and it becomes farther from the image sensing surface atthe tele-photo end conversely, θ₁>θ₂. Note that the light ray incidentangle at an intermediate angle of view assumes a value between theangles θ₁ and θ₂.

In the tele-photo zoom lens shown in FIGS. 16 and 17, when the stop ZSis set in an open aperture state, a light ray that strikes an off-axisimage sensing position passes through an offset position on the stopsurface. Hence, when the stop ZS is stopped down, the light ray incidentangle onto the image sensing surface changes.

FIGS. 18 and 19 are views showing the optical paths at the wide-angleend and tele-photo end when the stop ZS is substantially stopped down toa point aperture. An angle θ₃ shown in FIG. 18 is an incident angle of alight beam which strikes a maximum-angle-of-view position at thewide-angle end, and an angle θ₄ shown in FIG. 19 is an incident angle ofa light beam which strikes a maximum-angle-of-view position at thetele-photo end. The magnitude relationship among the light beams whichstrike the maximum-angle-of-view positions are:θ₃>θ₁>θ₄>θ₂In consideration of the degree of aperture of the stop ZS as well as thefocal length, the variation width of the incident angle furtherbroadens. The difference between the maximum and minimum angles fallswithin the range from 10° to 40°, although it depends on the zoom ratioand lens arrangement.

A change in incident angle of light rays that strikes off-axis positionstakes place not only in zooming but also focusing (focus adjustment).FIGS. 20 and 21 are views showing the arrangement of a macro lens as oneof image sensing lenses assembled in the lens device 126, and exemplifya lens which has a small f-number value (bright) and is suited to asingle-lens reflex camera. FIG. 20 shows a state wherein a focus isadjusted to an object at the infinity, and FIG. 21 shows a state whereina focus is adjusted to an object at the near distance (an imagingmagnification=−0.2×). The focal length and f-number of the macro lensare 50 mm and 2.0, and includes first to third groups MG1 to MG3 in turnfrom the object side. Reference symbol MS denotes a stop.

The macro lens includes the first group MG1 having positive refractingpower, the stop MS, the second group MG2 having positive refractingpower, and the third group MG3 having positive refracting power. Thefirst group MG1 includes a double-concave negative lens 611 which isarranged at a position closest to the object side, and the third groupMG3 includes a negative meniscus lens 632 which is arranged at aposition closest to the image side. The negative lenses 611 and 632sandwich a so-called Gaussian type lens system between them, and adouble-convex positive lens 612, a positive lens 613 having a surfacewith a stronger curvature facing the object side, a double-concavenegative lens 614, a double-concave negative lens 621, a positive lens622 cemented to the negative lens 621, a double-convex positive lens623, and a positive meniscus lens 631 form the Gaussian type lens. Thestop MS is arranged between the first and second groups MG1 and MG2. Byarranging the negative lenses before and after the Gaussian type lenssystem, the entrance pupil and exit pupil get closer to each other, thusobtaining a sufficient marginal light amount.

Furthermore, this macro lens has a floating mechanism so as to obtainsatisfactory optical performance for any of an object at the infinity tothat at the near distance. Upon focusing on an object at the neardistance from focusing on an object at the infinity, the first andsecond groups MG1 and MG2 are extended together, and the third group MG3is extended to increase the air space from the second group MG2.

Since the exit pupil position varies upon focusing, the incident angleof a light ray that strikes an off-axis image sensing position changesaccording to the set focal length. An angle θ₅ shown in FIG. 20 is anincident angle when a light beam that strikes the maximum-angle-of-viewposition is represented by its light amount barycenter while focusing onan object at the infinity. An angle θ₆ shown in FIG. 21 is an incidentangle when a light beam that strikes the maximum-angle-of-view positionis represented by its light amount barycenter while focusing on anobject at the near distance. Since the exit pupil position becomescloser to the image sensing surface upon focusing on an object at theinfinity, and is separated away from the image sensing surface uponfocusing on an object at the near distance, θ₅>θ₆. Note that the lightray incident angle when an object is at an intermediate distancenormally assumes a value between the angles θ₅ and θ₆.

In consideration of the degree of aperture of the stop MS as well as thedistance to the object, the variation width of the incident anglefurther broadens. The difference between the maximum and minimum anglesfalls within the range from 3° to 30°, although it depends on thenearest object distance that can be focused and lens arrangement.

The structure of the image sensing element 116 will be describe belowusing FIGS. 22 to 25.

FIG. 22 is a plan view of the image sensing element 116 shown in FIG.14. Referring to FIG. 22, reference numeral 116 denotes an image sensingelement; and 124, a sensor package that houses the image sensing element116. The image sensing element 116 is a CMOS image sensing element, andis formed by regularly arranging several million pixels in the verticaland horizontal directions or oblique directions so as to obtain imagedata for several million pixels. Therefore, the interior of the sensorpackage is filled up with low refractive index fluid having a refractiveindex of about 1.27 such as air, inert gas, or hydrofluoro ether.

FIG. 23 is a partial sectional view of the image sensing element 116.FIG. 23 is a partially enlarged view of a peripheral portion of theimage sensing element 116, in which the optical axis of the imagesensing element 116 is located on the left side of this figure, andmicrolenses decenter in the left direction of this figure. Various typesof color filter arrangements are available, and a Bayer arrangement isadopted in this case.

Referring to FIG. 23, reference numeral 70 denotes a green color filterwhich transmits green light; and 71, a red color filter which transmitsred light. In the section of the image sensing element with the Bayerarrangement, one of a row in which the green and red color filters arealternately arranged, as shown in FIG. 23, or a row in which blue andgreen color filters are alternately arranged appears.

Reference numeral 30 denotes a silicon substrate; 31, a photoelectricconversion unit of each of embedded photodiodes which are regularlyarranged at a pitch L; 32, a polysilicon wiring layer; 33 and 34, copperwiring layers; and 38, an insulating interlayer formed of, e.g.,hydrophobic porous silica or the like. The metal wiring layers sandwichthe insulating interlayer to form a kind of capacitor, which induces asignal delay. Hence, the dielectric constant of the porous silica is setto be lower than a silicon oxide film (SiO₂) which is popularly used inthe conventional elements. Since the refractive index is proportional tothe square of the dielectric constant, the refractive index is as low asabout 1.3.

Reference numeral 36 denotes an embedded transparent resin layer; and35, a protection film formed of a silicon oxynitride film (SiON).

The embedded transparent resin layer 36 is fabricated in the followingprocesses. That is, the potential structure, the photoelectricconversion unit 31, a MOS transistor amplifier, a pixel selectiontransistor, the copper wiring layers 33 and 34, the insulatinginterlayer 38, and the like in silicon are formed first. After theprotection film 35 is grown on the upper layer of that multilayeredstructure, anisotropic etching is applied from above the projection film35 toward the photoelectric conversion unit 31 to form an opening. Then,a liquid transparent resin is filled into this opening and is thermallyset.

The refractive index of the transparent resin layer 36 is 1.6, and formsa light guide to have a refractive index difference of about 1.2 timesfrom the refractive index (1.3) of the insulating interlayer 38 thatneighbors the transparent resin layer 36. Light rays which obliquelyenter this boundary surface beyond a critical angle from the highrefractive index side toward the low refractive index side is totallyreflected at the boundary surface between the transparent resin layer 36and the insulating interlayer 38.

Note that the embedded transparent resin layer 36 can be a compositematerial prepared by uniformly dispersing titanium oxide (TiO₂)particles, or silicon nitride (Si₃N₄) particles, niobium pentoxide(Nb₂O₅) particles or the like of nano scale into a base resin. With suchcomposite material, since the titanium oxide particles, silicon nitrideparticles, or niobium pentoxide particles have a size sufficientlysmaller than the wavelength of light, and the refractive index is ashigh as 2.35 for titanium oxide particles, 2.0 for silicon nitrideparticles, or 2.2 for niobium pentoxide particles, the refractive indexcan be pulled up to about 1.8 to 2.1 times from the refractive index(1.3) of the insulating interlayer 38 while maintaining rectilinearpropagation of light inside the composite material, thus greatlyreducing the critical angle that causes total reflection.

Reference numerals 37 and 39 denote flattening layers; and 902, a microconvex lens. The flattening layer 37 is a transparent resin layer formedon the projection layer 35 and transparent resin layer 36. The microconvex lens 902 made of SiON is formed by etching the upper portion ofthe flattening layer 39 in a concave shape, forming a silicon oxynitride(SiON) layer on it, and etching its top surface in a convex shape. Eachmicro convex lens 902 has a square shape when viewed from the opticalaxis direction, and both the upper and lower surfaces of each microconvex lens 902 are aspherical surfaces which have axial symmetry. FIG.24 is a view for explaining the shapes of the convex lenses 902, i.e., abird's-eye view of the micro convex lenses 902 viewed from obliquelyabove.

Since the refractive index of the flattening layer 39 is 1.58 and thatof the micro convex lens 902 is 1.8, the micro convex lens 902 has afocal length as a convergence system. Therefore, even when there isintervals between the neighboring embedded transparent resin layers 36,a light beam passes through the micro convex lenses 902 which are beddedwithout any interval, and is efficiently focused on any of the embeddedtransparent resin layers 36. Note that the micro convex lenses 902 maybe fabricated by welding a resin which is molded into a cylindricalshape by etching.

In general, since the wiring layers and the like are present near thephotoelectric conversion unit of the CMOS image sensing element, and acharge transfer unit and the like are present in the CCD image sensingelement, light rays which obliquely travel inside the image sensingelement hardly reach the photoelectric conversion unit. Light rays thatcannot reach the photoelectric conversion unit are absorbed by thewiring layers and the like and are eventually converted into heat.

As described above, the image sensing element 116 comprises the lightguide structure that guides such light rays which obliquely travelinside the image sensing element 116 to the photoelectric conversionunit 31. FIG. 25 is a ray-tracing diagram typically showing the opticalpath of a light beam which enters a micro convex lens 902 a of those ofthe light beam that enters the image sensing element 116.

Light rays 60 which come from above of the image sensing element 116enter the micro convex lens 902 a, undergo a refraction effect, and thenenter an embedded transparent resin layer 36 a via the flattening layer37. Since the embedded transparent resin layer 36 a has a refractiveindex higher than that of the insulating interlayer 38, light rays thatobliquely enter beyond the critical angle are totally reflected by theboundary surface between the resin layer 36 a and the insulatinginterlayer 38, and cannot leave the embedded transparent resin layer 36a to the insulating interlayer 38. More specifically, light rays 62 aretotally reflected by a boundary surface 64 between the embeddedtransparent resin layer 36 a and insulating interlayer 38, and stayinside the embedded transparent resin layer 36 a as light rays 63. Then,the light rays 63 enter a photoelectric conversion unit 31 a and arephotoelectrically converted.

The relationship between the behavior of light rays in the light guideand the pupil position has been explained above with reference to FIGS.2, 4, and 5. In the second embodiment as well, when the image sensingoptical system 125 is “close” to the image sensing element 116, i.e.,when the pupil distance is short and the incident angle θ of a lightbeam 330 is large (θ=α1), as shown in FIG. 4, the light beam 330 istotally reflected by the slope of the light guide 203. On the otherhand, when the pupil distance is long and the incident angle θ of thelight beam 330 is small (θ=α2), as shown in FIG. 5, the light beam 330is not reflected by the slope, and is guided to the photoelectricconversion unit 201.

In this manner, the light beam can be guided to the photoelectricconversion unit using the light guide structure even when the incidentangle θ changes.

Therefore, light rays, which cannot enter the photoelectric conversionunit 31 due to deviation of the exit pupil position from the imagesensing element upon zooming or focusing when no embedded transparentresin layer 36 is formed, can enter the photoelectric conversion unit 31using the light guide structure based on the embedded transparent resinlayer 36 shown in FIG. 25, thus improving the sensitivity of the imagesensing element on the periphery of the frame. Therefore, shading due tothe image sensing element can be eliminated.

The structure of the light guide is determined based on the followingproperties as in the first embodiment.

1. If the image height H increases, the incident angle θ becomes larger.

2. If the pupil distance L increases, the incident angle θ becomessmaller.

3. The critical angle that causes total reflection at the boundarysurface between the light guide and the insulating interlayer decreaseswith decreasing N_(L)/N_(H), i.e., the ratio of the refractive indexN_(L) Of the insulating interlayer to the refractive index N_(H) Of thelight guide, and light rays incident at a larger incident angle θ can becaptured.

4. If the pixel pitch P decreases, an area occupied by a circuit portionof each pixel increases, the photoelectric conversion unit sizedecreases relatively, and light rays incident at a larger incident angleθ cannot be captured. In case of the CMOS type solid-state image sensingelement, the circuit portion includes a charge transfer MOS transistor,a reset MOS transfer for supplying a reset potential, a source-followerMOS sensor transistor, a selection MOS transistor for selectivelyoutputting a signal from the source-follower MOS sensor transistor, andthe like.

5. If the height D from the photoelectric conversion unit to themicrolens increases, an angle at which the photoelectric conversion unitcan be seen from the microlens decreases, and light rays with a largerincident angle θ cannot be captured.

As can be seen from these properties, an evaluation value E, which isexpressed by the image height H, pupil distance L, pixel pitch P, heightD, refractive index N_(H) of the light guide, and refractive index N_(L)of the insulating interlayer, and is given by:

$\begin{matrix}{E = \frac{H \cdot D \cdot N_{L}}{L \cdot P \cdot N_{H}}} & (6)\end{matrix}$can be an index suited to express the amount of light rays with largeincident angle θ that can be guided to the photoelectric conversionunit.

For example, when

-   -   image height H=4251 [μm];    -   pupil distance L=15000 [μm];    -   pixel pitch P=3.25 [μm];    -   height D=5.0 [μm];    -   refractive index N_(L) of insulating interlayer 211=1.46; and    -   refractive index N_(H) of the light guide=1.65, E=0.39. In this        way, the effect the light guide structure is great when the        image height H, pupil distance L, pixel pitch P, height D,        refractive index N_(H) of the light guide, and refractive index        N_(L) of the insulating interlayer are selected to meet:        E<1.0  (7)        <Third Embodiment>

The light guide can be formed by combining other materials.

In the third embodiment, in the color image sensing element with thestructure shown in FIG. 23, the insulating interlayer 38 is formed ofsilicon oxide (SiO₂) and the embedded transparent layer 36 is formed ofsilicon nitride (Si₃N₄) unlike in the second embodiment.

Since the refractive index of the embedded transparent layer 36 is 2.0and that of silicon oxide (SiO₂) that forms the insulating interlayer 38that neighbors the embedded transparent layer 36 (silicon nitride) is1.46, a refractive index difference of about 1.37 times is generated.For this reason, light rays that obliquely enter the boundary surfacebeyond the critical angle from the high refractive index side toward thelow refractive index side can be totally reflected. With such lightguide structure, obliquely coming light is efficiently guided to thephotoelectric conversion unit 31.

Furthermore, in the third embodiment, the flattening layer 39 is formedusing silicon oxide (SiO₂), and the micro convex lens 902 of titaniumoxide (TiO₂) is formed by etching the upper portion of the flatteninglayer 39 in a concave shape, forming a titanium oxide (TiO₂) layer ontop of the etched flattening layer 39, and etching the upper surface ofthe titanium oxide layer in a convex shape.

Since the refractive index of silicon oxide (SiO₂) that forms theflattening layer 39 is 1.46, and that of titanium oxide (TiO₂) thatforms the micro convex lens 902 is 2.35, the micro convex lens 902 has afocal length as a convergence system. Therefore, even when there isintervals between the neighboring embedded transparent resin layers 36,a light beam passes through the micro convex lenses 902 which are beddedwithout any interval, and is efficiently focused on any of embeddedtransparent resin layers (silicon nitride) 36.

In this way, the same effect as in the second embodiment can be obtainedby combining different materials.

Note that a silicon oxynitride (SiON) film may be used in place ofsilicon nitride that forms the light guide. When silicon oxynitride(SiON) is used, since the residual stress can be reduced, theprobability of occurrence of film peeling or the like lowers, and themanufacturing yield of the image sensing element can be improved.

<Fourth Embodiment>

The light guide can also be formed by combining still other materials.Also, an intra-layer lens can be formed using a low refractive indexlayer in the image sensing element.

FIG. 26 is a sectional view of some pixels of a color image sensingelement with a light guide according to the fourth embodiment of thepresent invention. In FIG. 26, photoelectric conversion units eachhaving a layer structure are formed unlike in the first and secondembodiments.

Referring to FIG. 26, reference numeral 340 denotes a silicon substrate;331B, 331G, and 331R, photoelectric conversion units of an embeddedphotodiode; 332, a polysilicon wiring layer; 333 and 334, copper wiringlayers; and 338, hydrophobic porous silica as an insulating interlayer.Reference numeral 336 denotes an embedded silicon oxide (SiO₂) layer;and 335, a protection film formed of a silicon oxynitride film (SiON).

The photoelectric conversion unit 331B photoelectrically converts lightof the entire visible range, the photoelectric conversion unit 331Gmainly photoelectrically converts green light and red light, and thephotoelectric conversion unit 331R mainly photoelectrically converts redlight. The arrangement which comprises three photoelectric conversionunits having different spectral sensitivities per pixel is free fromoccurrence of any false color since object image sampling positions forrespective colors match upon obtaining a color image.

The embedded silicon oxide layer 336 is fabricated in the followingprocesses. That is, the potential structure, the photoelectricconversion units 331B, 331G, and 331R, a MOS transistor amplifier, apixel selection transistor, the copper wiring layers 333 and 334, theinsulating interlayer 338, and the like in silicon are formed first.After the protection film 335 is grown on the upper layer of thatmultilayered structure, anisotropic etching is applied from above theprojection film 335 toward the photoelectric conversion unit 331 to forman opening. Then, silicon oxide (SiO₂) is embedded in this opening by aCVD device.

The refractive index of the embedded silicon oxide layer 336 is 1.46,and has a refractive index different about 1.12 times of that (1.3) ofthe insulating interlayer that neighbors the embedded silicon oxidelayer 336. Hence, the embedded silicon oxide layer 336 can totallyreflect light rays which obliquely enter this boundary surface beyondthe critical angle from the high refractive index side toward the lowrefractive index side. With this light guide structure, obliquelyincoming light is efficiently guided to the photoelectric conversionunits 331B, 331G, and 331R.

Furthermore, reference numeral 337 denotes a flattening layer; 90, anintra-layer lens; and 339, a flattening layer formed of a transparentresin. The flattening layer 337 is formed of silicon oxynitride (SiON)which is formed on the protection layer 335 and embedded silicon oxidelayer 336. The intra-layer lens 90 of hydrophobic porous silica isformed by etching the upper portion of the flattening layer 337, forminga hydrophobic porous silica layer on that upper portion, and thenetching the upper surface of the hydrophobic porous silica layer in aconcave shape. Each intra-layer lens 90 has a square shape when viewedfrom the optical axis direction, and both the upper and lower surfacesof each intra-layer lens 90 are aspherical surfaces which have axialsymmetry.

Since the refractive index of the flattening layer 337 is 1.80, that ofthe intra-layer lens 90 is 1.30, and that of the flattening layer 339 is1.58, the intra-layer lens 90 has a focal length as a convergence systemalthough it is a double-concave lens. Therefore, even when there isintervals between the neighboring embedded silicon oxide layers 336, alight beam passes through the intra-layer lenses 90 which are beddedwithout any interval, and can be efficiently focused on any of theembedded silicon oxide layers 336.

FIG. 26 includes a ray-tracing diagram that typically shows the opticalpath of a light beam which enters an intra-layer lens 90 a. Light rays360 that enter the intra-layer lens 90 a are refracted by theintra-layer lens 90 a, and then enter an embedded silicon oxide layer336 a via the flattening layer 337. Since the embedded silicon oxidelayer 336 a has a higher refractive index than that of the insulatinginterlayer 338, light rays that obliquely enter beyond the criticalangle are totally reflected by the boundary surface between the embeddedsilicon oxide layer 336 a and the insulating interlayer 338, and cannotleave the embedded silicon oxide layer 336 a to the insulatinginterlayer 338. More specifically, light rays 362 are totally reflectedby a boundary surface 364 between the embedded silicon oxide layer 336 aand insulating interlayer 338, and stay inside the embedded siliconoxide layer 336 a as light rays 363. Then, the light rays 363 enter aphotoelectric conversion unit 331 a and are photoelectrically converted.

As described above, according to the fourth embodiment, the same effectas in the second embodiment can be obtained.

Note that the second to fourth embodiments have explained the lightguide structure which causes total reflection by utilizing therefractive index difference of materials. Alternatively, a light guideusing metal surface reflection may be used. Also, a gap sealed with agas or a vacuum gap may be used in place of the insulating interlayer.

<Fifth Embodiment>

The fifth embodiment of the present invention will be described below.

Since the fifth embodiment uses the lens-exchangeable digital camerasystem which has been explained using FIGS. 31 and 12, a descriptionthereof will be omitted.

In such lens-exchangeable digital camera system, since the exit pupilposition varies depending on the focal length or the like of anexchangeable lens mounted on the camera body 1200, a light beam that canbe received by, especially, pixels of a peripheral portion of the imagesensor 1208, changes depending on the exchangeable lens to be mounted.

FIG. 27 is an element sectional view of the CMOS solid-state imagesensing element 200 used as the image sensor 1208 of the camera body1200, which is arranged on the prospective imaging surface of thewide-angle lens 420. As shown in FIG. 27, the image sensing element 200has a light guide. Note that the same reference numerals in FIG. 27denote the same parts as in FIG. 3.

Referring to FIG. 27, reference numeral 201 denotes a photoelectricconversion unit; 202, a silicon (Si) substrate on which thephotoelectric conversion unit 201 is formed; and 203, a light guide madeof SiN or the like as a material having a high refractive index. Thecentral axis of the light guide 203 substantially agrees with that ofthe photoelectric conversion unit 201. The light entrance side of thelight guide 203 is formed to have a broader opening so as to receivemore light components. Reference numeral 210 denotes a transferelectrode which is formed in an insulating interlayer 211 made of SiO₂or the like with a low refractive index, and is used to transfer a photocharge generated by the photoelectric conversion unit 201 to a floatingdiffusion (FD) unit (not shown); and 204 and 205, wiring electrodeswhich are formed to selectively read out charges generated by thephotoelectric conversion unit 201. Normally, the transfer electrode 210is made of polysilicon (Poly-Si), and the wiring electrodes 204 and 205are made of aluminum (Al).

Reference numeral 206 denotes a flattening layer which is formed on anuneven surface due to electrodes and wiring layers (not shown) toprovide a flat surface. A color filter 207 is formed on the flatteninglayer 206, and a microlens 209 is also formed on the flattening layer208. The microlens 209 is arranged to efficiently focus light comingfrom the exchangeable lens 420 on the photoelectric conversion unit 201.

In FIG. 27, light transmitted through the microlens 209 passes throughthe flattening layer 208, and undergoes wavelength selection in thecolor filter layer 207. For example, when the color filter layer 207 ofthe left pixel in FIG. 27 transmits a green light component, blue andred light components are absorbed. When the color filter layer 207 ofthe right pixel in FIG. 27 transmits a blue light component, green andred light components are absorbed. Light of a predetermined wavelength,which has been transmitted through the color filter layer 207 istransmitted through the light guide 203 formed of a transparent materialwith a high refractive index (refractive index N_(H)) such as siliconnitride (SiN) or the like, and is guided to the photoelectric conversionunit 201. Since the insulating interlayer 211 is formed around the lightguide 203 using a transparent material with a low refractive index(refractive index N_(L)) such as silicon oxide (SiO₂) or the like, lightthat goes from the light guide 203 toward the insulating interlayer 211is totally reflected by a boundary surface between the light guide 203and insulating interlayer 211, and is guided to the photoelectricconversion unit 201. The refractive index N_(L) of the insulatinginterlayer 211 formed of silicon oxide (SiO₂) is, e.g., 1.46.

Let P be the spacing (pixel pitch) between neighboring pixels, and D bethe height from the apex of the microlens 209 to the photoelectricconversion unit 201.

The light collecting characteristics of the solid-state image sensingelement 200 with the light guide, as shown in FIG. 27, are as hasalready been described above with reference to FIGS. 2, 4, and 5. Incase of the solid-state image sensing element 200 with the light guide203, as shown in FIG. 4, even when the indent angle θ=α1 of an objectlight beam 330 with respect to an optical axis 321 is large (when thepupil distance L is short), the light is totally reflected by a slope ofthe light guide 203, and is efficiently guided to the photoelectricconversion unit 201.

When the pupil distance L of the image sensing optical system 101 islong and the indent angle θ=α2 of the object light beam 330 with respectto the optical axis 321 is small, as shown in FIG. 5, the object light330 directly enters the photoelectric conversion unit 201 without beingreflected by the slope of the light guide 203.

In order to improve the focusing effect even in case of an object lightbeam which has a large incident angle to the solid-state image sensingelement 200, the structure of the light guide is determined based on thefollowing properties.

1. If the image height H increases, the incident angle θ becomes larger.

2. If the pupil distance L increases, the incident angle θ becomessmaller.

3. The critical angle that causes total reflection at the boundarysurface between the light guide and the insulating interlayer decreaseswith decreasing N_(L)/N_(H), i.e., the ratio of the refractive indexN_(L) of the insulating interlayer to the refractive index N_(H) of thelight guide, and light rays incident at a larger incident angle θ can becaptured.

4. If the pixel pitch P decreases, an area occupied by a circuit portionof each pixel increases, the photoelectric conversion unit sizedecreases relatively, and light rays incident at a larger incident angleθ cannot be captured. In case of the CMOS type solid-state image sensingelement, the circuit portion includes a charge transfer MOS transistor,a reset MOS transfer for supplying a reset potential, a source-followerMOS sensor transistor, a selection MOS transistor for selectivelyoutputting a signal from the source-follower MOS sensor transistor, andthe like.

5. If the height D from the photoelectric conversion unit to themicrolens increases, an angle at which the photoelectric conversion unitcan be seen from the microlens decreases, and light rays with a largerincident angle θ cannot be captured.

As can be seen from these properties, an evaluation value E, which isexpressed by the image height H, pupil distance L, pixel pitch P, heightD, refractive index N_(H) of the light guide, and refractive index N_(L)of the insulating interlayer, and is given by:

$\begin{matrix}{E = \frac{H \cdot D \cdot N_{L}}{L \cdot P \cdot N_{H}}} & (6)\end{matrix}$can be an index suited to express the amount of light rays with largeincident angle θ that can be guided to the photoelectric conversionunit. Note that the effect of the light guide structure is great whenthe image height H, pupil distance L, pixel pitch P, height D,refractive index N_(H) of the light guide, and refractive index N_(L) ofthe insulating interlayer are selected to meet:E<1.0  (7)

It is ideal that the lens-exchangeable digital camera system uses asolid-state image sensing element having a light guide that canefficiently focus object light independently of an exchangeable lensmounted on the camera body. The light guide is formed based oninequality (2) using lens information of an exchangeable lens that canbe mounted on the camera.

In the lens-exchangeable digital camera system shown in FIG. 12 in thefifth embodiment, the frame size of the image sensor 1208 to be mountedis substantially equal to the APS-C size (about 17×25 mm) as the filmsize of a silver halide camera. Hence, the image height H of pixelslocated at corners of the frame is about 15 mm.

Also, the height D from the apex of the microlens to the photoelectricconversion unit of the solid-state image sensing element used in theimage sensor 1208 is about 0.006 mm.

The insulating interlayer filled around the light guide formed in theimage sensor 1208 normally uses silicon oxide (SiO₂), and its refractiveindex N_(L) is 1.46. Also, the light guide is normally formed of siliconnitride (SiN), and its refractive index N_(H) is 2.0. Note that siliconoxide and silicon nitride are merely an example, and the presentinvention is not limited to these specific materials.

FIG. 13 is an explanatory view of an incoming light beam to the imagesensor 1208 when the image sensor using the solid-state image sensingelement with the aforementioned structure is applied to thelens-exchangeable digital camera system shown in FIG. 12. In FIG. 13,the wide-angle lens 420 is mounted as the exchangeable lens.

In FIG. 13, an exit pupil 425 of the retrofocus type wide-angle lens 420is formed at the position of a distance L_(w) close to the image sensor1208. An object light beam that has been transmitted through the exitpupil 425 of the wide-angle lens 420 enters the image sensor 1208 at theposition of the image height H. At this time, an incident angle θ_(w) ofa chief ray to the image sensor 1208 satisfies:tan θ_(w) =H/L _(w)

FIG. 11 is an explanatory view of incoming light to the image sensor1208 which is arranged in the digital camera system which mounts thetele-photo lens 1220 shown in FIG. 17 as an exchangeable lens.

As shown in FIG. 11, an exit pupil 1225 of the tele-photo lens 1220 isformed at the position of a distance L_(t) farther from the image sensor1208 than when the wide-angle lens 420 shown in FIG. 12 is mounted. Anobject light beam that has been transmitted through the exit pupil 1225enters the sensor 1208 at the position of the image height H. At thistime, an incident angle θ_(t) of a chief ray to the image sensor 1208satisfies:tan θ_(t) =H/L _(t)

As can be seen from FIGS. 11 and 13, the chief ray angle θ_(w) when thewide-angle lens is mounted on the camera and the chief ray angle θ_(t)when the tele-photo lens is mounted meet:θ_(w)>θ_(t)and the incident angle θ of the chief ray to the image sensor 1208 whenthe wide-angle lens is mounted is larger. Therefore, the structure ofthe light guide is determined using exit pupil information of a lenswhich has a shorter exit pupil distance from the image field ofexchangeable lenses that can be mounted on the camera. If the exit pupildistance L of a lens having a shorter exit pupil distance from the imageheight of the exchangeable lenses that can be mounted on the camera isabout 60 mm (other conditions are the same as those described above),the relationship between the pixel pitch P of the image sensor 1208 andthe evaluation value E is calculated based on equation (6) by:E×P=0.0011 [mm]Since the resolution improves with decreasing pixel pitch P of the imagesensor 1208, if the pixel pitch P is set to be 0.003 mm, the evaluationvalue E is:E=0.37which satisfies inequality (7).

In this way, when the light guide of the solid-state image sensingelement 200 to be mounted on the lens-exchangeable digital camera systemis formed to satisfy equation (6) and inequality (7) using exchangeablelens information, light transmitted through the light guide is totallyreflected by the boundary surface between the light guide and theinsulating interlayer and is efficiently focused on the photoelectricconversion unit. As a result, a high-quality image can be obtained, anda high-resolution image can also be obtained since a solid-state imagesensing element with a smaller pixel size can be adopted.

In the fifth embodiment, the structure of the light guide formed in thesolid-state image sensing element is determined based on the exit pupilinformation of an exchangeable lens that can be mounted on the camera.Also, it is effective to determine the structure of the light guide inconsideration of an open F-value in addition to the exit pupilinformation of an exchangeable lens.

As described above, according to the fifth embodiment, in thelens-exchangeable digital camera system, since the light collectingefficiency is improved by forming the light guide that considers themoving range of the exit pupils of exchangeable lenses above thephotoelectric conversion unit of the solid-state image sensing element,a high-quality image can be obtained. In addition, a high-resolutionimage can be obtained by reducing the pixel size per pixel.

<Other Embodiments>

The invention can be implemented by supplying a software program, whichimplements the function of executing a simulation for designating asolid-state image sensing element described in the first embodiment,directly or indirectly to a system or apparatus, reading the suppliedprogram code with a computer of the system or apparatus, and thenexecuting the program code. In this case, so long as the system orapparatus has the functions of the program, the mode of implementationneed not rely upon a program.

Accordingly, since the functions of the present invention areimplemented by computer, the program code installed in the computer alsoimplements the present invention. In other words, the claims of thepresent invention also cover a computer program for the purpose ofimplementing the functions of the present invention.

In this case, so long as the system or apparatus has the functions ofthe program, the program may be executed in any form, such as an objectcode, a program executed by an interpreter, or scrip data supplied to anoperating system.

Example of storage media that can be used for supplying the program area floppy disk, a hard disk, an optical disk, a magneto-optical disk, aCD-ROM, a CD-R, a CD-RW, a magnetic tape, a non-volatile type memorycard, a ROM, and a DVD (DVD-ROM and a DVD-R).

As for the method of supplying the program, a client computer can beconnected to a website on the Internet using a browser of the clientcomputer, and the computer program of the present invention or anautomatically-installable compressed file of the program can bedownloaded to a recording medium such as a hard disk. Further, theprogram of the present invention can be supplied by dividing the programcode constituting the program into a plurality of files and downloadingthe files from different websites. In other words, a WWW (World WideWeb) server that downloads, to multiple users, the program files thatimplement the functions of the present invention by computer is alsocovered by the claims of the present invention.

It is also possible to encrypt and store the program of the presentinvention on a storage medium such as a CD-ROM, distribute the storagemedium to users, allow users who meet certain requirements to downloaddecryption key information from a website via the Internet, and allowthese users to decrypt the encrypted program by using the keyinformation, whereby the program is installed in the user computer.

Besides the cases where the aforementioned functions according to theembodiments are implemented by executing the read program by computer,an operating system or the like running on the computer may perform allor a part of the actual processing so that the functions of theforegoing embodiments can be implemented by this processing.

Furthermore, after the program read from the storage medium is writtento a function expansion board inserted into the computer or to a memoryprovided in a function expansion unit connected to the computer, a CPUor the like mounted on the function expansion board or functionexpansion unit performs all or a part of the actual processing so thatthe functions of the foregoing embodiments can be implemented by thisprocessing.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments thereof except as defined in the appended claims.

CLAIM OF PRIORITY

This application claims priority from Japanese Patent Application Nos.2004-114360 filed on Apr. 8, 2004, 2004-210379 filed on Jul. 16, 2004and 2004-214617, filed on Jul. 22, 2004, which are hereby incorporatedby reference herein.

1. A solid-state image sensing element having a photoelectric conversionelement which converts incoming light into an electrical signal inaccordance with an amount of the light, a microlens which is arranged onan incident surface, a light guide which is arranged between thephotoelectric conversion element and the microlens, and an insulatinginterlayer which is arranged around the light guide, wherein saidsolid-state image sensing element located at a distance (H) satisfies:$\frac{H \cdot D}{L \cdot P} < {{a \cdot \frac{N_{H}}{N_{L}}}{\mspace{11mu}\;}{for}\mspace{14mu} 0} < a < 1$where L is a distance from an exit pupil of an image sensing opticalsystem of an image sensing device, which mounts an image sensor formedby two-dimensionally arranging a plurality of said solid-state imagesensing elements, H is a distance from a center of the image sensor to aposition of said solid-state image sensing element on the image sensor,D is a height from said photoelectric conversion element to an apex ofthe microlens, P is a spacing between the plurality of solid-state imagesensing elements, N_(H) is a refractive index of the light guide, andN_(L) is a refractive index of the insulating interlayer.
 2. A designsupport method for supporting to design a solid-state image sensingelement having a photoelectric conversion element which convertsincoming light into an electrical signal in accordance with an amount ofthe light, a microlens which is arranged on an incident surface, a lightguide which is arranged between the photoelectric conversion element andthe microlens, and an insulating interlayer which is arranged around thelight guide, comprising: a condition acquisition step of acquiring atleast some of conditions including a distance L from an exit pupil of animage sensing optical system of an image sensing device, which mounts animage sensor formed by two-dimensionally arranging a plurality of saidsolid-state image sensing elements, a distance H from a center of theimage sensor to a position of said solid-state image sensing element onthe image sensor, a height D from the photoelectric conversion elementto an apex of the microlens, a spacing P between the plurality ofsolid-state image sensing elements, a refractive index N_(H) of thelight guide, and a refractive index N_(L) of the insulating interlayer;a determination step of determining if all the conditions can beacquired in said condition acquisition step; a calculation step ofcomputing, when it is determined in the determination step that all theconditions can be acquired,$\frac{H \cdot D}{L \cdot P} < {a \cdot \frac{N_{H}}{N_{L}}}$ andcalculating a; a computing step of computing, when it is determined inthe determination step that all the conditions cannot be acquired, avalue which satisfies 0<a<1 for a condition which cannot be acquired;and a notifying step of notifying the calculated a value or the valuecomputed in the computing step.
 3. The method according to claim 2,wherein the distance H is a distance from the center of the image sensorto the solid-state image sensing element which is located at a mostperipheral position of the image sensor.
 4. The method according toclaim 2, wherein the exit pupil position of the image sensing opticalsystem of the image sensing device can be changed, and the distance L isa distance from the exit pupil position closest to the image sensor. 5.The method according to claim 2, wherein the image sensing opticalsystem of the image sensing device is exchangeable, and the distance Lis a distance from the exit pupil position closest to the image sensorwhen an image sensing optical system, which has an exit pupil closest tothe image sensor of image sensing optical systems that can be mounted onthe image sensing device, is mounted.
 6. A storage medium which isreadable by an information processing apparatus storing a program whichcan be executed by the information processing apparatus and has aprogram code for implementing a design support method of claim
 2. 7. Adesign support apparatus for supporting to design a solid-state imagesensing element having a photoelectric conversion element which convertsincoming light into an electrical signal in accordance with an amount ofthe light, a microlens which is arranged on an incident surface, a lightguide which is arranged between the photoelectric conversion element andthe microlens, and an insulating interlayer which is arranged around thelight guide, comprising: a condition acquisition unit that acquires atleast some of conditions including a distance L from an exit pupil of animage sensing optical system of an image sensing device, which mounts animage sensor formed by two-dimensionally arranging a plurality of saidsolid-state image sensing elements, a distance H from a center of theimage sensor to a position of said solid-state image sensing element onthe image sensor, a height D from the photoelectric conversion elementto an apex of the microlens, a spacing P between the plurality ofsolid-state image sensing elements, a refractive index N_(H) of thelight guide, and a refractive index N_(L) of the insulating interlayer;a determination unit that determines if all the conditions can beacquired by said condition acquisition unit; a computing unit thatcomputes, when said determination unit determines that all theconditions can be acquired,$\frac{H \cdot D}{L \cdot P} < {a \cdot \frac{N_{H}}{N_{L}}}$ andcalculates a, and that computes, when said determination unit determinesthat all the conditions cannot be acquired, a value which satisfies0<a<1 for a condition which cannot be acquired; and a notifying unitthat notifies the calculated a value or the value computed by saidcomputing unit.
 8. A solid-state image sensing element comprising: aphotoelectric conversion element which converts incoming light into anelectrical signal in accordance with an amount of the light; a microlenswhich is arranged on an incident surface; a light guide which isarranged between said photoelectric conversion element and saidmicrolens, and is formed of a composite material prepared by dispersingin resin one of titanium oxide (TiO₂), silicon nitride (Si₃N₄), andniobium pentoxide (Nb₂O₅); and an insulating interlayer which isarranged around said light guide and is formed of hydrophobic poroussilica, wherein said solid-state image sensing element located at adistance (H) satisfies:$\frac{H \cdot D}{L \cdot P} < {{a \cdot \frac{N_{H}}{N_{L}}}{\mspace{11mu}\;}{for}\mspace{14mu} 0} < a < 1$where L is a distance from an exit pupil of an image sensing opticalsystem of an image sensing device, which mounts an image sensor formedby two-dimensionally arranging a plurality of said solid-state imagesensing elements, H is a distance from a center of the image sensor to aposition of said solid-state image sensing element on the image sensor,D is a height from said photoelectric conversion element to an apex ofsaid microlens, P is a spacing between the plurality of solid-stateimage sensing elements, N_(H) is a refractive index of said light guide,and N_(L) is a refractive index of said insulating interlayer.
 9. Theelement according to claim 8, further comprising a flattening layerwhich is arranged between said microlens and said light guide, and isformed of silicon oxide (SiO₂), wherein said microlens is formed oftitanium oxide (TiO₂).
 10. The element according to claim 8, furthercomprising a flattening layer which is arranged between said microlensand said light guide, and is formed of silicon oxynitride (SiON),wherein said microlens is a double-concave intra-layer lens formed ofhydrophobic porous silica.
 11. The element according to claim 8, whereinsaid photoelectric conversion element is formed of a plurality ofphotoelectric conversion layers having different spectral sensitivities.12. A solid-state image sensing element comprising: a photoelectricconversion element which converts incoming light into an electricalsignal in accordance with an amount of the light; a microlens which isarranged on an incident surface; a light guide which is arranged betweensaid photoelectric conversion element and said microlens, and is formedof a material selected from silicon nitride (Si₃N₄) and siliconoxynitride (SiON); and an insulating interlayer which is arranged aroundsaid light guide and is formed of silicon oxide (SiO₂), wherein saidsolid-state image sensing element located at a distance (H) satisfies:$\frac{H \cdot D}{L \cdot P} < {{a \cdot \frac{N_{H}}{N_{L}}}{\mspace{11mu}\;}{for}\mspace{14mu} 0} < a < 1$where L is a distance from an exit pupil of an image sensing opticalsystem of an image sensing device, which mounts an image sensor formedby two-dimensionally arranging a plurality of said solid-state imagesensing elements, H is a distance from a center of the image sensor to aposition of said solid-state image sensing element on the image sensor,D is a height from said photoelectric conversion element to an apex ofsaid microlens, P is a spacing between the plurality of solid-stateimage sensing elements, N_(H) is a refractive index of said light guide,and N_(L) is a refractive index of said insulating interlayer.
 13. Theelement according to claim 12, further comprising a flattening layerwhich is arranged between said microlens and said light guide, and isformed of silicon oxide (SiO₂), wherein said microlens is formed oftitanium oxide (TiO₂).
 14. The element according to claim 12, furthercomprising a flattening layer which is arranged between said microlensand said light guide, and is formed of silicon oxynitride (SiON),wherein said microlens is a double-concave intra-layer lens formed ofhydrophobic porous silica.
 15. The element according to claim 12,wherein said photoelectric conversion element is formed of a pluralityof photoelectric conversion layers having different spectralsensitivities.
 16. A solid-state image sensing element comprising: aphotoelectric conversion element which converts incoming light into anelectrical signal in accordance with an amount of the light; a microlenswhich is arranged on an incident surface; a light guide which isarranged between said photoelectric conversion element and saidmicrolens, and is formed of silicon oxide (SiO₂); and an insulatinginterlayer which is arranged around said light guide and is formed ofhydrophobic porous silica, wherein said solid-state image sensingelement located at a distance (H) satisfies:$\frac{H \cdot D}{L \cdot P} < {{a \cdot \frac{N_{H}}{N_{L}}}{\mspace{11mu}\;}{for}\mspace{14mu} 0} < a < 1$where L is a distance from an exit pupil of an image sensing opticalsystem of an image sensing device, which mounts an image sensor formedby two-dimensionally arranging a plurality of said solid-state imagesensing elements, H is a distance from a center of the image sensor to aposition of said solid-state image sensing element on the image sensor,D is a height from said photoelectric conversion element to an apex ofsaid microlens, P is a spacing between the plurality of solid-stateimage sensing elements, N_(H) is a refractive index of said light guide,and N_(L) is a refractive index of said insulating interlayer.
 17. Theelement according to claim 16, further comprising a flattening layerwhich is arranged between said microlens and said light guide, and isformed of silicon oxide (SiO₂), wherein said microlens is formed oftitanium oxide (TiO₂).
 18. The element according to claim 16, furthercomprising a flattening layer which is arranged between said microlensand said light guide, and is formed of silicon oxynitride (SiON),wherein said microlens is a double-concave intra-layer lens formed ofhydrophobic porous silica.
 19. The element according to claim 16,wherein said photoelectric conversion element is formed of a pluralityof photoelectric conversion layers having different spectralsensitivities.
 20. An image sensing apparatus which has a solid-stateimage sensing element having a photoelectric conversion element whichconverts incoming light into an electrical signal in accordance with anamount of the light, a microlens which is arranged on an incidentsurface, a light guide which is arranged between the photoelectricconversion element and the microlens, and an insulating interlayer whichis arranged around the light guide, comprising: an attachment/detachmentunit that allows an exchangeable lens to attach/detach to/from saidimage sensing apparatus, wherein said solid-state image sensing elementlocated at a distance (H) satisfies:$\frac{H \cdot D}{L \cdot P} < {{a \cdot \frac{N_{H}}{N_{L}}}{\mspace{11mu}\;}{for}\mspace{14mu} 0} < a < 1$where L is a distance from an exit pupil of an image sensing opticalsystem of an image sensing device, which mounts an image sensor formedby two-dimensionally arranging a plurality of said solid-state imagesensing elements, H is a distance from a center of the image sensor to aposition of said solid-state image sensing element on the image sensor,D is a height from said photoelectric conversion element to an apex ofthe microlens, P is a spacing between the plurality of solid-state imagesensing elements, N_(H) is a refractive index of the light guide, andN_(L) is a refractive index of the insulating interlayer.